0000950170-24-022055 | 10-K | XBRL Viewer

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Income Taxes - Summary of Components of Expense for (Benefit) from Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
U.S. federal	$ 1,640	$ 1,815	$ 173
U.S. state	710	768	73
Total current tax expense	2,350	2,583	246
U.S. federal	595	(1,148)	(5)
U.S. state	247	(476)	(2)
Total deferred tax expense (benefit)	842	(1,624)	(7)
Total income tax expense	$ 3,192	$ 959	$ 239

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Investments in Debt Securities

12 Months Ended

Dec. 31, 2023

Debt Securities [Abstract]

Investments in Debt Securities

3. Investments in Debt Securities

Debt securities are classified in the consolidated balance sheet as follows:


		December 31,
		2023		2022
		Balance		Balance
	(in thousands)
Cash equivalents		$	24,273	$	18,404
Current marketable securities			150,130		142,480
Non-current marketable securities			57,312		36,457
Total		$	231,715	$	197,341

The following table summarizes debt securities by maturity at December 31, 2023 (in thousands):


Maturity	Amortized Cost
Within one year	$	174,403
After one year through five years		57,312
Total	$	231,715

The following table summarizes debt securities by credit-quality indicator:


	Credit Quality Indicator as of December 31, 2023
	AAA		AA- to AA+		A- to A+		Total
	(In thousands)
Money market funds	$	24,273	$	—	$	—	$	24,273
Corporate paper and notes		—		33,526		112,889		146,415
U.S. government agency securities		4,000		27,482		7,974		39,456
U.S. treasuries		—		20,585		986		21,571
Total	$	28,273	$	81,593	$	121,849	$	231,715

The credit quality indicator was derived from publicly available ratings published by Moody’s or a comparable credit rating agency, last updated as of December 31, 2023.

The following table summarizes the fair value of debt securities by major security type held at December 31, 2023 (in thousands):


Description	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	24,273	$	—	$	—		$	24,273
Corporate paper and notes		146,415		425		(148	)		146,692
U.S. government agency securities		39,456		24		(70	)		39,410
U.S. treasuries		21,571		18		(19	)		21,570
Total	$	231,715	$	467	$	(237	)	$	231,945

The following table summarizes the fair value of debt securities by major security type held at December 31, 2022 (in thousands):


Description	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	18,404	$	—	$	—		$	18,404
Corporate paper and notes		126,102		15		(736	)		125,381
U.S. government agency securities		34,364		4		(181	)		34,187
U.S. treasuries		18,471		—		(98	)		18,373
Total	$	197,341	$	19	$	(1,015	)	$	196,345

The allowance for credit losses applicable to debt securities was immaterial in all periods presented.

Fair Value

The fair value of money market funds is determined based on publicly available market price for these funds (Level 1). The fair value of other debt securities is determined based on the publicly available inputs which includes a market price for the same or similar instruments adjusted for estimates in interest yield (Level 2).

Intangible Assets, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Amortization of intangible assets	$ 215	$ 304	$ 240

Accrued Expenses and Other Liabilities - Summary of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued research and development expenses	$ 27,970	$ 26,159
Accrued personnel costs	8,348	5,778
Accrued general and administrative expenses	2,129	3,615
Other	35	38
Accrued expenses	$ 38,482	$ 35,590

Employee Benefit Plans - Intrinsic Value of Stock Options Exercised and Vested RSUs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate intrinsic value of options exercised	$ 3,937	$ 1,369
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total fair value of RSUs vested	$ 238	$ 423

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of Preparation

The Company prepared its consolidated financial statements in compliance with generally accepted accounting principles in the U.S. ("U.S. GAAP"). Any reference in these notes to applicable guidance is meant to refer to authoritative U.S. GAAP as found in the Accounting Standards Codification ("ASC") and Accounting Standards Update ("ASU") of the Financial Accounting Standards Board ("FASB").

Principles of Consolidation

Subsidiaries are entities controlled by the Company, consisting of Merus N.V.’s wholly owned subsidiary Merus US, Inc. The Company controls an entity when it is exposed to, or has rights to, variable returns from its involvement with the entity and has the ability to affect those returns through its power over the entity. The financial statements of subsidiaries are included in the consolidated financial statements from the date on which control commences until the date on which control ceases. All significant intercompany balances and transactions have been eliminated in consolidation.

Functional and Presentation Currency

Items recorded in each of the Company’s entities are measured using the currency of the primary economic environment in which the entity operates (the "functional currency"). Merus US, Inc.’s functional currency is the U.S. dollar. The functional currency of Merus N.V. is the euro. After measuring foreign currency denominated transactions into an entity’s functional currency, to the extent that a subsidiary’s functional currency differs from its parent, a subsidiary’s financial position and results of operations are translated into its parent’s functional currency. The Company’s consolidated financial position and results of operations are translated into the U.S. dollar as the Company’s reporting currency.

Use of Estimates

The preparation of these consolidated financial statements in accordance with U.S. GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities, as of the date of the consolidated financial statements, and the reported amounts of collaboration revenue and expenses during the reporting period. Actual results and outcomes may differ materially from management’s estimates, judgments and assumptions.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to concentrations of credit risk include cash, cash equivalents, marketable securities and accounts receivable. The Company attempts to minimize the risks related to cash, cash equivalents and marketable securities by working with highly rated financial institutions that invest in a broad and diverse range of financial instruments as defined by the Company. The Company has established guidelines relative to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. The Company maintains its funds in accordance with its investment policy, which defines allowable investments, specifies credit quality standards and is designed to limit the Company’s credit exposure to any single issuer.

Accounts receivable represent amounts due from collaboration partners. The Company monitors economic conditions to identify facts or circumstances that may indicate that any of its accounts receivable are at risk of collection.

Subsequent Events

The Company considers events or transactions that occur after the balance sheet date but before the consolidated financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The Company evaluated all events and transactions through the date these financial statements were filed with the Securities and Exchange Commission.

Fair Value Measurements

Fair value is defined as an exit price, representing the amount that would be received upon the sale of an asset or payment to transfer a liability in an orderly transaction between market participants. Fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or liability. A three-tier fair value hierarchy is used to prioritize the inputs in measuring fair value as follows:

•

Level 1 – Quoted market prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date.

•

Level 2 – Quoted market prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable, either directly or indirectly. Fair value determined through the use of models or other valuation methodologies.

•

Level 3 – Significant unobservable inputs for assets or liabilities that cannot be corroborated by market data. Fair value is determined by the reporting entity’s own assumptions utilizing the best information available and includes situations where there is little market activity for the asset or liability.

The asset’s or liability’s fair value measurement within the fair value hierarchy is based upon the lowest level of any input that is significant to the fair value measurement.

The Company considers its cash, cash equivalents, accounts receivable, marketable securities due with maturities 12 months or less, and accounts payable financial instruments to reflect their fair value given their short maturity and risk profile of the counterparty.

Going Concern

At each reporting period, the Company evaluates whether there are conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company is required to make certain additional disclosures if it concludes substantial doubt exists and it is not alleviated by the Company’s plans or when its plans alleviate substantial doubt about the Company’s ability to continue as a going concern.

The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs, and comparing those needs to the current cash, cash equivalent and marketable security balances. After considering the Company’s current research and development plans and the timing expectations related to the progress of its clinical-stage programs and its plans to pursue commercialization of any antibody candidate, if approved, and after considering its existing cash, cash equivalents and marketable securities as of December 31, 2023, the Company did not identify conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year from the date these financial statements were issued. Additional details of the Company’s cash runway are described in Note 1 The Company.

Cash and Cash Equivalents

The Company considers all highly liquid debt securities with original final maturities of three months or less from the date of purchase to be cash equivalents. Instruments subject to restrictions are not included in cash and cash equivalents.

Restricted Cash

The Company maintains certain cash balances restricted to withdrawal or use. Restricted cash includes cash held as collateral for certain contractual agreements and is recorded in other assets in the consolidated balance sheets.

Marketable Securities

The Company classifies marketable securities that are debt securities with a remaining maturity when purchased of greater than three months as held-to-maturity as the Company has the positive intent and ability to hold such debt securities through maturity.

Debt securities that are classified as held-to-maturity are initially recognized and measured at fair value. Subsequent to initial recognition, they are measured at amortized cost using the effective interest rate method. Interest income from these debt securities is included in interest income. Marketable securities are classified as current if their expected maturity is within one year or less of the balance sheet date and non-current if their maturity is beyond one year of the balance sheet date.

Accounts Receivable

Accounts receivable are amounts due from collaboration partners as a result of research and development services provided or milestones achieved but not yet paid.

Allowance for Credit Losses

The Company evaluates its cash equivalents, accounts receivable and held-to-maturity marketable securities financial assets for expected credit losses. Expected credit losses represent the portion of the amortized cost basis of a financial asset that an entity does not expect to collect. An allowance for expected credit losses is meant to reflect a risk of loss even if remote, irrespective of the expectation of collection from a particular issuer or debt security. The Company has not historically experienced any credit losses on any of its financial assets.

With respect to cash equivalents and accounts receivable, given consideration of their short maturity, lack of historical losses and the current environment, the Company concluded there is generally no expected credit losses for these financial assets. With respect to held-to-maturity marketable securities which are comprised of debt securities, the Company evaluates expected credit losses on a pooled basis based on issuer-type which have similar credit risk characteristics. The allowance for credit losses is immaterial for all periods presented.

Property and Equipment

The Company records property and equipment at cost. The Company calculates depreciation and amortization using the straight-line method over the following estimated useful lives:


Asset Category		Useful Lives
Laboratory equipment		5 years
Office furniture and equipment		5 years
Leasehold improvements		Shorter of term of lease or 10 years

The Company capitalizes expenditures for new property and equipment and improvements to existing facilities and charges the cost of maintenance to expense. The Company eliminates the cost of property retired or otherwise disposed of, along with the corresponding accumulated depreciation or amortization, from the related accounts, and the resulting gain or loss is reflected in the results of operations.

Intangible Assets

Intangible assets are identifiable non-monetary assets without physical substance. An asset is a resource that is controlled by the enterprise as a result of past events (for example, purchase or self-creation) and from which future economic benefits (inflows of cash or other assets) are expected. The useful lives of intangible assets are assessed to be definite-lived and amortized over the useful economic life. The Company’s intangible assets are comprised of purchased licenses to intellectual property and software licenses.

Impairment of Long-Lived Assets

The Company reviews long-lived assets to be held and used, including property and equipment, operating lease right-of-use assets and definite-lived intangible assets, for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets or asset group may not be recoverable.

Evaluation of recoverability is first based on an estimate of undiscounted future cash flows resulting from the use of the asset or asset group and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the asset or asset group, the assets are written down to their estimated fair values. No such impairments were recorded in 2023, 2022 or 2021.

Leases

The Company determines if an arrangement is or contains a lease at inception. For leases with a term of 12 months or less, the Company does not recognize a right-of-use asset or lease liability. The Company does not have any finance leases.

Right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease, and excludes non-lease payments. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. As the Company’s leases typically do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments.

Operating lease right-of-use assets also include the effect of any lease payments made and excludes lease incentives. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. Operating lease expense is recognized on a straight-line basis over the lease term.

The Company has real estate operating lease agreements with lease and non-lease components, which are generally accounted for separately as operating lease costs and variable lease costs. Non-lease components in real estate leases refer to services provided by the lessor related to the premises. Fixed and variable lease payments are both allocated to lease and non-lease components. The allocation is determined on a relative fair value basis of the services provided relative to the operating lease of premises. With respect to equipment leases, the Company has elected not to allocate payments amongst lease and non-lease components as a practical expedient as afforded under ASC 842, Leases.

Income Taxes

Deferred Taxes

The Company records deferred taxes to recognize the future effects of temporary differences between the tax basis and financial statement carrying amount of assets and liabilities. The Company measures the deferred taxes using enacted tax rates expected to apply when the temporary differences are realized and records a valuation allowance to reduce deferred tax assets if it is determined that it is more likely than not that all or a portion of the deferred tax asset will not be realized. The Company considers many factors when assessing the likelihood of future realization of deferred tax assets, including recent earnings results, expectations of future taxable income, carryforward periods available, reversing taxable temporary differences and other relevant factors. The Company records changes in the required valuation allowance in the period that the determination is made.

Unrecognized Tax Benefits

The Company assesses its income tax positions and records tax benefits for all years subject to examination based upon management’s evaluation of the technical merits, facts, circumstances and information available as of the reporting date. For those tax positions where it is more likely than not that a tax benefit will be sustained, the Company records the largest amount of tax benefit with a greater than 50.0% likelihood of being realized upon settlement with a taxing authority having full knowledge of all relevant information. For those income tax positions where it is not more likely than not that a tax benefit will be sustained, the Company does not recognize a tax benefit in the financial statements. The Company records interest and penalties related to an underpayment of income taxes, if applicable, as a component of income tax expense.

Revenue Recognition

The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for an arrangement, the Company performs the following five step analysis:

identify the contract(s) with a customer;

ii.

identify the performance obligations in the contract;

iii.

determine the transaction price;

iv.

allocate the transaction price to the performance obligations in the contract; and

recognize revenue when (or as) the entity satisfies a performance obligation.

The Company has entered into collaboration and license agreements, which are within the scope of ASC 606, Revenue from Contracts with Customers, to discover, develop, manufacture and commercialize product candidates. The terms of these agreements typically contain multiple promises or obligations, which may include: (i) licenses, or options to obtain licenses, to product candidates or future product candidates directed to specific targets (referred to as “exclusive licenses”) and (ii) research and development activities to be

performed on behalf of the collaboration partner related to the licensed targets. The Company also derives revenue from government grants.

As part of the accounting for these arrangements, the Company must use judgment to determine:

the number of performance obligations based on the determination under step (ii) above and whether those performance obligations are distinct from other performance obligations in the contract;

the transaction price under step (iii) above;

the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above;

whether the combined performance obligation is satisfied over time or at a point in time in step (v) above; and

the appropriate method for measuring progress toward complete satisfaction of a performance obligation in step (v) above.

The Company uses judgment to determine whether milestones or other variable consideration, except for sales-based royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. The Company recognizes variable consideration when the constraint has been resolved. Based on the nature of the variable consideration related to milestones, the Company allocates the variable amount (and subsequent changes to that amount) entirely to a performance obligation or to a distinct good or service that forms a part of a single performance obligation. In validating its estimated stand-alone selling price, the Company evaluates whether changes in the key assumptions used to determine its estimated stand-alone selling price will have a significant effect on the allocation of arrangement consideration between performance obligations.

Amounts received prior to revenue recognition are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. Amounts recognized as revenue, but not yet received or invoiced are generally recognized as unbilled receivables.

Exclusive Licenses

If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, which generally include research and development services, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license.

In assessing whether a license is distinct from the other promises, the Company considers relevant facts and circumstances of each arrangement, including the rights and obligations set out in the contract, the research and development capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from the license for its intended purpose without the receipt of the remaining promises, whether the value of the license is dependent on the unsatisfied promises, whether there are other vendors that could provide the remaining promises, and whether it is separately identifiable from the remaining promises.

For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue.

The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the research and development and licensing agreement.

The Company’s arrangements may provide the collaboration partner with the right to select a target for licensing either at the inception of the arrangement or in the future. Under these arrangements, fees may be due to the Company (i) at the inception of the arrangement as an upfront fee or payment, (ii) upon the exercise of an option to acquire a license or (iii) upon extending the selection period as an extension fee or payment. If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the goods and services underlying the customer options are not considered to be performance obligations at the outset of the arrangement, as they are contingent upon option exercise. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the inception of the arrangement. The Company allocates the transaction price to material rights based on the relative stand-alone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised or expires.

For arrangements that include sales-based milestones and royalties, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any sales-based milestones or royalty revenue resulting from any of its arrangements.

Research and Development Services

The promises under the Company’s collaboration and license agreements generally include research and development services to be performed by the Company on behalf of the collaboration partner. For performance obligations that include research and development services, the Company recognizes revenue allocated to such performance obligations based on an appropriate measure of progress. The Company utilizes judgment to determine the appropriate method of measuring progress for purposes of recognizing revenue, which is generally an input measure such as costs incurred. The Company evaluates the measure of progress each reporting period as described under Exclusive Licenses above.

Reimbursements from the partner are evaluated as to whether the Company acts as a principal or an agent in such relationships. The Company evaluates whether control over the underlying goods or services were obtained prior to transferring these goods or services to the collaboration partner. Where the Company does not control the goods or services prior to transferring these goods or services to the collaboration partner, such reimbursements are presented net of costs.

At the inception of each arrangement that includes development milestone payments in respect of development efforts, the Company evaluates whether the development milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated development milestone value is included in the transaction price. Development milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular development milestone in making this assessment. There is judgment involved in determining whether it is probable that a significant revenue reversal would not occur.

At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of all development milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. If a milestone or other variable consideration relates specifically to the Company’s efforts to satisfy a single performance obligation or to a specific outcome from satisfying the performance obligation, the Company generally allocates the milestone amount entirely to that performance obligation once it is probable that a significant revenue reversal would not occur.

Government Grants

The Company receives certain government and regional grants, which support its research efforts in defined projects, and include contributions towards the R&D cost. When there is reasonable assurance that the Company will comply with the conditions attached to a received grant, and when there is reasonable assurance that the grant will be received, government grants are recognized as revenue on a gross basis in the consolidated statement of profit or loss and comprehensive loss on a systematic basis over the periods in which the Company recognizes expenses for the related costs for which the grants are intended to compensate. In the case of grants related to assets, the received grant will be deducted from the carrying amount of the asset. Government grant revenue may be subject to review by a government authority in periods subsequent to their recognition and may result in the reversal of grant revenue previously recognized. Reversals of grant revenue are presented as contra revenue in the consolidated statement of operations.

Research and Development Expenses

Research and development expenses are expensed as incurred. Research and development expenses are comprised of costs incurred in providing research and development activities, including salaries and benefits, facilities costs, overhead costs, contract research and development services, and other outside costs. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made.

When third-party service providers’ billing terms do not coincide with the Company’s period-end, the Company is required to make estimates of its obligations to those third parties, including clinical trial and pharmaceutical development costs, contractual services costs and costs for supply of its product candidates incurred in a given accounting period and record accruals at the end of the period. The Company bases its estimates on its knowledge of the research and development programs, services performed for the period, past history in conducting similar activities and the expected duration of the third-party service contract, among other considerations.

The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. There may be instances in which payments made to vendors will exceed the level of services provided and result in a prepayment of research and development expenses.

The WBSO (afdrachtvermindering speur- en ontwikkelingswerk) is a Dutch fiscal facility that provides subsidies to companies, knowledge centers and self-employed people who perform research and development activities (as defined in the WBSO Act). Under this act, a contribution is paid towards the labor costs of employees directly involved in research and development. For the years ended December 31, 2023, 2022 and 2021, the Company recognized $6.3 million, $5.9 million and $9.3 million as a reduction of research and development expenses, respectively.

Share-Based Compensation

The Company measures employee share-based compensation based on the grant date fair value of the share-based compensation award. The Company grants stock options at exercise prices equal to the fair value of the Company’s common stock on the date of grant, based on observable market prices.

For share-based awards subject time-based vesting, the Company recognizes employee share-based compensation expense on a straight-line basis over the requisite service period of the awards, generally from the date of grant through each vesting date. The Company recognizes forfeitures at the time they occur. The actual expense recognized over the vesting period will only represent those options that vest; the effect of forfeitures in the recognition of periodic compensation expense are not estimated prior to their occurrence.

Earnings (Loss) per Share

The Company computes basic earnings (loss) per share by dividing income (loss) allocable to common stockholders by the weighted average number of shares of common stock outstanding. During periods of income, the Company allocates participating securities a proportional share of income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities. During periods of loss, the Company allocates no loss to participating securities because they have no contractual obligation to share in the losses of the Company. The Company computes diluted earnings (loss) per share after giving consideration to the dilutive effect of stock options and restricted stock units (“RSU”) that are outstanding during the period, except where such non-participating securities would be anti-dilutive.

Segment Information

The Company operates in one reportable segment, which comprises the discovery and development of innovative therapeutics.

Recently Adopted Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the FASB or other standard‑setting bodies that are adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

In August 2018, the FASB issued ASU No. 2018-2, Financial Services—Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts, which is aimed at improving the Codification related to long-duration contracts which will improve the timeliness of recognizing changes in the liability for future policy benefits, simplify accounting for certain market-based options, simplify the amortization of deferred acquisition costs, and improve the effectiveness of required disclosures. The FASB delayed the effective date of ASU 2018-12 to periods beginning after December 15, 2022, and interim periods within those fiscal years. This ASU is effective for the Company beginning January 1, 2023, and interim periods within that year. The Company adopted

and applied the amendments of this ASU to its disclosures. The application of this ASU did not have a material impact on the Company's financial position, results of operations or cash flows.

In October 2021, the FASB issued ASU 2021-08, Business Combination (Topic 805): Accounting for Contract Assets and Contract Liabilities from Contracts with Customers. This guidance amends ASC 805 to “require acquiring entities to apply Topic 606 to recognize and measure contract assets and contract liabilities in a business combination.” Under current GAAP, an acquirer generally recognizes such items at fair value on the acquisition date. This ASU is effective for the Company beginning January 1, 2023, and interim periods within that year. The Company adopted and applied the amendments of this ASU to its disclosures. The application of this ASU did not have a material impact on the Company's financial position, results of operations or cash flows.

In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which expands annual and interim disclosure requirements for reportable segments, primarily through enhanced disclosures about significant segment expenses. ASU 2023-07 is effective for annual periods beginning December 15, 2023, and for interim periods beginning after December 15, 2024, with early adoption permitted. The Company is currently evaluating the potential effect that the updated standard will have on its financial statement disclosures.

Stockholders' Equity - Additional Information (Details)							1 Months Ended	12 Months Ended
Stockholders' Equity - Additional Information (Details)	Aug. 14, 2023 USD ($)	Aug. 09, 2023 $ / shares shares	May 22, 2023 USD ($)	Nov. 09, 2021 USD ($) $ / shares shares	Jan. 21, 2021 USD ($) $ / shares shares	Jan. 18, 2021 USD ($) $ / shares shares	May 31, 2021 USD ($)	Dec. 31, 2023 USD ($) shares	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2023 € / shares shares	Aug. 09, 2023 € / shares	Dec. 31, 2022 € / shares shares
Class Of Stock [Line Items]
Common stock voting rights								one vote
Issuance of common stock, net										$ 248,058,000
Common shares, issued \| shares											57,825,879		46,310,589
Common shares, par value \| € / shares											€ 0.09		€ 0.09
Sales Agreement
Class Of Stock [Line Items]
Issuance of common stock,net, shares \| shares								3,272,280
Issuance of common stock, net			$ 124,900,000					$ 63,800,000
Proceeds from issuance of common stock, net								$ 65,500,000	$ 59,500,000
Common shares, issued \| shares													2,720,846
Sales agent commissions									$ 1,700,000
Underwriting Agreement
Class Of Stock [Line Items]
Issuance of common stock,net, shares \| shares		6,818,182
Sale of Stock, Price Per Share \| $ / shares		$ 22
Issuance of common stock, net	$ 162,200,000
Common shares, par value \| € / shares												€ 0.09
Additional common shares at public offering price \| shares		1,022,727
Maximum \| Sales Agreement
Class Of Stock [Line Items]
Stock sale agreement authorized amount			$ 125,000,000				$ 125,000,000
Underwriting commissions rate of gross proceeds of shares sold							3.00%
Underwritten Public Offering
Class Of Stock [Line Items]
Issuance of common stock,net, shares \| shares				4,438,597	5,575,757	706,834
Sale of Stock, Price Per Share \| $ / shares				$ 28.5	$ 24.75	$ 28.295
Proceeds from issuance of common stock, net				$ 118,700,000	$ 129,400,000	$ 16,500,000

Employee Benefit Plans - Summary of RSU Activity (Details) - RSUs	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of RSUs, Non-vested, Beginning balance \| shares	25,000
Number of RSUs, Granted \| shares	20,000
Number of RSUs, Vested \| shares	(10,000)
Number of RSUs, Forfeited \| shares	(15,000)
Number of RSUs, Non-vested, Ending balance \| shares	20,000
Weighted Average Grant-date Fair Value, Non-vested, Beginning balance \| $ / shares	$ 21.87
Weighted Average Grant-date Fair Value, Granted \| $ / shares	21.20
Weighted Average Grant-date Fair Value, Vested \| $ / shares	24.61
Weighted Average Grant-date Fair Value, Forfeited \| $ / shares	20.04
Weighted Average Grant-date Fair Value, Non-vested, Ending balance \| $ / shares	$ 21.20

Income Taxes - Summary of Components of Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 161,966	$ 110,722
Deferred revenue	10,903	17,593
Research and development costs	0	1,419
Excess interest carryforward	84	1,316
Lease obligation	3,160	3,507
Accrued expenses and other	1,238	696
Total deferred tax assets	177,351	135,253
Deferred tax asset valuation allowance	(173,152)	(129,848)
Total deferred tax assets, net of valuation allowance	4,199	5,405
Deferred tax liabilities:
Operating lease right-of-use assets	2,953	3,286
Other	47	79
Total deferred tax liabilities	3,000	3,365
Net deferred tax asset	$ 1,199	$ 2,041

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 204,246	$ 147,749
Marketable securities	150,130	142,480
Accounts receivable	2,429	4,051
Prepaid expenses and other current assets	12,009	12,163
Total current assets	368,814	306,443
Marketable securities	57,312	36,457
Property and equipment, net	12,135	12,222
Operating lease right-of-use assets	11,362	12,618
Intangible assets, net	1,800	1,950
Deferred tax assets	1,199	2,041
Other assets	2,872	4,811
Total assets	455,494	376,542
Current liabilities:
Accounts payable	4,602	9,834
Accrued expenses and other liabilities	38,482	35,590
Income taxes payable	1,646	2,400
Current portion of lease obligation	1,674	1,684
Current portion of deferred revenue	22,685	29,418
Total current liabilities	69,089	78,926
Lease obligation	10,488	11,790
Deferred revenue, net of current portion	19,574	38,771
Total liabilities	99,151	129,487
Commitments and contingencies (Note 10)
Stockholders’ equity:
Common shares, EUR 0.09 par value; 67,500,000 and 67,500,000 shares authorized at December 31, 2023 and 2022, respectively; 57,825,879 46,310,589 shares issued and outstanding at December 31, 2023 and 2022, respectively	5,883	4,751
Additional paid-in capital	1,126,054	870,874
Accumulated deficit	(753,061)	(598,122)
Accumulated other comprehensive (loss) income	(22,533)	(30,448)
Total stockholders’ equity	356,343	247,055
Total liabilities and stockholders’ equity	$ 455,494	$ 376,542

Collaborations - Summary of Company's Accompanying Consolidated Financial Statements Attributable to Transactions Arising From Collaboration Arrangements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in the period	$ 17,230	$ 16,776	$ 18,864
Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in the period	10,528	10,048	0
Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in the period	0	222	602
Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in the period	27,758	27,046	$ 602
Accounts Receivable \| Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Billings	12,374
Cash receipts	(12,395)
Foreign exchange	21
Accounts Receivable \| Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Billings	4,336
Cash receipts	(4,336)
Accounts Receivable \| Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2023	1,068
Billings	69
Cash receipts	(1,142)
Foreign exchange	5
Balance at December 31, 2023		1,068
Accounts Receivable \| Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2023	1,068
Billings	16,779
Cash receipts	(17,873)
Foreign exchange	26
Balance at December 31, 2023		1,068
Unbilled Receivables \| Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2023	1,986
Accrued receivables	11,778
Billings	(12,374)
Adjustments	7
Balance at December 31, 2023	1,397	1,986
Unbilled Receivables \| Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2023	808
Accrued receivables	4,374
Billings	(4,336)
Adjustments	(7)
Balance at December 31, 2023	839	808
Unbilled Receivables \| Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2023	189
Foreign exchange	4
Balance at December 31, 2023	193	189
Unbilled Receivables \| Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2023	2,983
Accrued receivables	16,152
Billings	(16,710)
Foreign exchange	4
Balance at December 31, 2023	2,429	2,983
Deferred Revenue \| Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Foreign exchange	1,496
Balance at January 1, 2023	52,059
Revenue recognized in the period	(17,230)
Balance at December 31, 2023	36,325	52,059
Less: current portion	(17,610)
Non-current balance at December 31, 2023	18,715
Deferred Revenue \| Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Foreign exchange	332
Balance at January 1, 2023	16,130
Revenue recognized in the period	(10,528)
Balance at December 31, 2023	5,934	16,130
Less: current portion	(5,075)
Non-current balance at December 31, 2023	859
Deferred Revenue \| Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Foreign exchange	1,828
Balance at January 1, 2023	68,189
Revenue recognized in the period	(27,758)
Balance at December 31, 2023	42,259	$ 68,189
Less: current portion	(22,685)
Non-current balance at December 31, 2023	$ 19,574

Investments in Debt Securities - Summary of Debt Securities by Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Held-to-Maturity, Amortized Cost, after Allowance for Credit Loss, Maturity, Allocated and Single Maturity Date [Abstract]
Within one year	$ 174,403
After one year through five years	57,312
Total	$ 231,715	$ 197,341

Operating Leases - Additional Information (Details) € in Millions	1 Months Ended		12 Months Ended
	Apr. 30, 2022 m² Renewalterm	Mar. 31, 2019	Dec. 31, 2023 USD ($)	Dec. 31, 2022 EUR (€)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2023 USD ($)	Apr. 05, 2022 EUR (€)	Apr. 05, 2022 USD ($)
Lessee Lease Description [Line Items]
Extended lease term						1 year 6 months
Operating lease, description						During the year ended December 31, 2021, the Company signed a lease amendment (the “Amendment”), which extended the term of the lease for its former corporate headquarters with Stichting Incubator Utrecht by approximately 1.5 years ending at the end of March 2023. The Amendment did not include additional right-of-use other than the extended lease term.
Operating lease, expiration period						March 2023
Additional renewal term						no
Operating lease, base rent			$ 2,367,000		$ 2,622,000
Operating lease right-of-use assets			11,362,000		$ 12,618,000
Operating lease liability			12,162,000
Lessee, Operating Lease, Liability, to be Paid, Total			$ 14,443,000			$ 100,000
Former Corporate Headquarters
Lessee Lease Description [Line Items]
Operating lease liability							$ 0
Kadans Science Partner XII BV \| Office Building
Lessee Lease Description [Line Items]
Extended lease term	10 years
Area of property available for operating lease \| m²	4,957
Operating lease, base rent \| €				€ 1.4
Operating lease right-of-use assets								€ 10.5	$ 11,500,000
Operating lease liability								11.3	12,400,000
Operating lease, renewal term	5 years
Operating lease, number of renewal term \| Renewalterm	2
Operating lease, termination term	20 years
Expected lease end date	Apr. 04, 2032
Operating lease, rent adjustment description	The rent amount is subject to adjustment based on the consumer price index (the “CPI”) annually, beginning one year after the lease commencement date, subject to certain limitations if the CPI is greater than 3.0%.
Lease incentive received								€ 0.8	$ 900,000
Incremental borrowing rate								4.85%	4.85%
Kadans Science Partner XII BV \| Minimum \| Office Building
Lessee Lease Description [Line Items]
Consumer price Index	3.00%
Merus US Inc
Lessee Lease Description [Line Items]
Extended lease term		7 years
Operating lease, description		Merus US, Inc. entered into a non-cancellable operating lease agreement for office space in Cambridge, Massachusetts. The lease commenced in the second quarter of 2019 and has a term of seven years, and may be extended for another five years. Given the Company’s current plans, the renewal term has not been included in the estimate of the lease term.
Operating lease, extended term of agreement		5 years
Operating lease, option to extend		true
Operating lease, options to extend description		may be extended for another five years.

The Company - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ (753,061)	$ (598,122)

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Intangible Assets, Net - Schedule of Expected Amortization Expense (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
2024	$ 164
2025	150
2026	150
2027	150
2028	150
Thereafter	1,036
Intangible assets, net	$ 1,800	$ 1,950

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ (154,939)	$ (131,194)	$ (66,816)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-8

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-9

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 13: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480167/946-830-55-10

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483581/946-220-45-7

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-Topic 944
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-Paragraph 1
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-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

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-Topic 946
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-Name Accounting Standards Codification
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-Paragraph 1
-Subparagraph (SX 210.6-07(9))
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+ Details

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Netherlands
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 2.3	$ 1.0	$ 1.2

Investments in Debt Securities (Tables)

12 Months Ended

Dec. 31, 2023

Debt Securities [Abstract]

Summary of Classification of Debt Securities in Consolidated Balance Sheet

Debt securities are classified in the consolidated balance sheet as follows:


		December 31,
		2023		2022
		Balance		Balance
	(in thousands)
Cash equivalents		$	24,273	$	18,404
Current marketable securities			150,130		142,480
Non-current marketable securities			57,312		36,457
Total		$	231,715	$	197,341

Summary of Debt Securities by Maturity

The following table summarizes debt securities by maturity at December 31, 2023 (in thousands):


Maturity	Amortized Cost
Within one year	$	174,403
After one year through five years		57,312
Total	$	231,715

Summary of Debt Securities by Credit Quality Indicator

The following table summarizes debt securities by credit-quality indicator:


	Credit Quality Indicator as of December 31, 2023
	AAA		AA- to AA+		A- to A+		Total
	(In thousands)
Money market funds	$	24,273	$	—	$	—	$	24,273
Corporate paper and notes		—		33,526		112,889		146,415
U.S. government agency securities		4,000		27,482		7,974		39,456
U.S. treasuries		—		20,585		986		21,571
Total	$	28,273	$	81,593	$	121,849	$	231,715

Summary of Fair Value of Debt Securities by Major Security Type

The following table summarizes the fair value of debt securities by major security type held at December 31, 2023 (in thousands):


Description	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	24,273	$	—	$	—		$	24,273
Corporate paper and notes		146,415		425		(148	)		146,692
U.S. government agency securities		39,456		24		(70	)		39,410
U.S. treasuries		21,571		18		(19	)		21,570
Total	$	231,715	$	467	$	(237	)	$	231,945

The following table summarizes the fair value of debt securities by major security type held at December 31, 2022 (in thousands):


Description	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Money market funds	$	18,404	$	—	$	—		$	18,404
Corporate paper and notes		126,102		15		(736	)		125,381
U.S. government agency securities		34,364		4		(181	)		34,187
U.S. treasuries		18,471		—		(98	)		18,373
Total	$	197,341	$	19	$	(1,015	)	$	196,345

- Definition

Tabular disclosure of information about investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5B

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (aaa)
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Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (d)
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-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 5A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5A

Reference 13: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 5A
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5A

Reference 14: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 5A
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Reference 15: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 16: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 17: http://www.xbrl.org/2009/role/commonPracticeRef
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Reference 18: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
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-Name Accounting Standards Codification
-Section 50
-Paragraph 5B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5B

+ Details

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Total revenue	$ 43,947	$ 41,586	$ 49,107
Operating expenses:
Research and development	140,658	149,424	98,187
General and administrative	59,836	52,200	40,896
Total operating expenses	200,494	201,624	139,083
Operating loss	(156,547)	(160,038)	(89,976)
Other income (loss), net:
Interest (expense) income, net	14,510	2,722	(129)
Foreign exchange (losses) gains, net	(9,710)	26,022	24,663
Other (losses) gains, net		1,059	(1,135)
Total other income (loss), net	4,800	29,803	23,399
Loss before income tax expense	(151,747)	(130,235)	(66,577)
Income tax expense	3,192	959	239
Net loss	(154,939)	(131,194)	(66,816)
Other comprehensive income (loss):
Currency translation adjustment	7,915	(21,227)	(18,292)
Comprehensive loss	$ (147,024)	$ (152,421)	$ (85,108)
Net loss per share attributable to common stockholders:
Basic	$ (3)	$ (2.92)	$ (1.73)
Diluted	$ (3)	$ (2.92)	$ (1.73)
Weighted-average common shares outstanding:
Basic	51,605,444	44,919,084	38,638,434
Diluted	51,605,444	44,919,084	38,638,434
Collaboration Revenue [Member]
Total revenue from contracts with customers	$ 43,947	$ 41,586	$ 19,503
Collaboration Revenue (Related Party) [Member]
Total revenue from contracts with customers	$ 0	$ 0	$ 29,604

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consists of the following:


	December 31,
	2023			2022
	(In thousands)
Laboratory equipment	$	7,489		$	6,349
Office equipment and furniture		2,052			1,872
Leasehold improvements		10,293			9,111
Construction in progress		44			75
Property and equipment		19,878			17,407
Less: accumulated depreciation and amortization		(7,743	)		(5,185	)
Property and equipment, net	$	12,135		$	12,222

The Company

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The Company

1. The Company

Merus N.V. is a clinical-stage oncology company developing innovative antibody therapeutics, headquartered in Utrecht, the Netherlands. Merus US, Inc. is a wholly-owned subsidiary of Merus N.V. located at 139 Main Street, Cambridge, Massachusetts, United States (collectively, the “Company”).

Since inception, the Company has generated an accumulated deficit of $753.1 million as of December 31, 2023. The Company expects to continue to incur significant expenses and operating losses for the foreseeable future as its antibody candidates advance through discovery, pre-clinical development and clinical trials and as it seeks regulatory approval and pursues commercialization of any approved antibody candidate.

As a result, the Company may need additional financing to support its continuing operations. Until the Company can generate significant revenue from product sales, if ever, the Company expects to finance its operations through public equity offerings, debt financings, or other sources, which may include collaborations, business development and licensing opportunities with third parties. Adequate additional financing may not be available to the Company on acceptable terms, or at all. The Company’s inability to raise capital as and when needed would have a negative impact on its financial condition and ability to pursue its business strategy. The Company will need to generate significant revenues to achieve profitability and may never do so.

Collaborations - Summary of Company's Collaboration Arrangements Earned in Period to Be Billed and Collected in Next Period (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative Arrangement, Revenue Not from Contract with Customer, Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax
Operating expenses:
Research and development	$ 140,658	$ 149,424	$ 98,187
General and administrative	59,836	52,200	40,896
Total operating expenses	200,494	201,624	139,083
Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments amortization	17,230	16,776	18,864
Reimbursement revenue	5,814	8,602	8,740
Milestones	5,980	1,000	2,000
Other	0	0
Total collaboration revenue	29,024	26,378	29,604
Operating expenses:
Research and development	24	752	1,223
General and administrative	0	0	0
Total operating expenses	24	752	1,223
Revenue recognized in the period	17,230	16,776	18,864
Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments amortization	10,528	10,281	14,012
Reimbursement revenue	4,339	3,634	3,332
Milestones	0	0	0
Other	0	0
Total collaboration revenue	14,867	13,915	17,344
Operating expenses:
Research and development	0	0	0
General and administrative	0	0	0
Total operating expenses	0	0	0
Revenue recognized in the period	10,528	10,048	0
Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments amortization	0	222	602
Reimbursement revenue	0	0	1,057
Milestones	0	1,021	500
Other	56	50
Total collaboration revenue	56	1,293	2,159
Operating expenses:
Research and development	0	0	151
General and administrative	0	0	0
Total operating expenses	0	0	151
Revenue recognized in the period	0	222	602
Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments amortization	27,758	27,279	14,614
Reimbursement revenue	10,153	12,236	4,389
Milestones	5,980	2,021	500
Other	56	50
Total collaboration revenue	43,947	41,586	19,503
Operating expenses:
Research and development	24	752	151
General and administrative	0	0	0
Total operating expenses	24	752	151
Revenue recognized in the period	$ 27,758	$ 27,046	$ 602

Accrued Expenses and Other Liabilities

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Accrued Expenses and Other Liabilities

7. Accrued Expenses and Other Liabilities

Accrued expenses consisted of the following:


	December 31,
	2023		2022
	(In thousands)
Accrued research and development expenses	$	27,970	$	26,159
Accrued personnel costs		8,348		5,778
Accrued general and administrative expenses		2,129		3,615
Other		35		38
Accrued expenses	$	38,482	$	35,590

Intangible Assets, Net (Tables)

12 Months Ended

Dec. 31, 2023

Intangible Assets, Gross (Excluding Goodwill) [Abstract]

Summary of Intangible Assets, Net

Intangible assets, net consists of the following:


	December 31,
	2023			2022
	(In thousands)
Licenses of intellectual property	$	3,565		$	3,441
Software licenses		184			251
Intangible assets		3,749			3,692
Less: accumulated amortization		(1,949	)		(1,742	)
Intangible assets, net	$	1,800		$	1,950

Schedule of Expected Amortization Expense

Amortization expense over the next five years is expected to be as follows (in thousands):


Year	Expected amortization
2024	$	164
2025		150
2026		150
2027		150
2028		150
Thereafter		1,036
Total remaining value	$	1,800

Loss per Share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Summary of Basic and Diluted Loss per Share

Basic and diluted loss per share allocable to common stockholders are computed as follows:


	Year Ended December 31,
	2023			2022			2021
	(In thousands except per share data)
Net loss	$	(154,939	)	$	(131,194	)	$	(66,816	)
Weighted average shares outstanding		51,605,444			44,919,084			38,638,434
Basic and diluted loss per share allocable to common stockholders	$	(3.00	)	$	(2.92	)	$	(1.73	)

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

10. Commitments and Contingencies

Indemnities

The Company indemnifies its officers and directors for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The maximum potential amount of future payments the Company could be required to make is unlimited; however, the Company has directors’ and officers’ insurance coverage that is intended to limit its exposure and enable it to recover a portion of any future amounts paid.

The Company enters into certain agreements with other parties in the ordinary course of business that contain indemnification provisions. These typically include agreements with directors and officers, business partners, contractors, landlords, clinical sites and customers. Under these provisions, the Company may indemnify and hold harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of the Company’s activities, such as gross negligence, willful misconduct or at times, other activities. These indemnification provisions may survive termination of the underlying agreements. The maximum potential amount of future payments the Company could be required to make under these indemnification provisions may be unlimited. However, to date the Company has not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these obligations is minimal. Accordingly, the Company did not have any liabilities recorded for these obligations as of December 31, 2023.

Litigation

From time to time, the Company may be involved in various claims and legal proceedings relating to or arising out of the Company’s operations. The Company is not currently a party to any material legal proceedings.

On August 19, 2022, Kymab Limited ("Kymab"), a subsidiary of Sanofi, filed a notice of opposition against the Company's EP3456190 patent (the "'190 patent"), entitled "Antibody Producing Transgenic Murine Animal," in the European Opposition Division of the European Patent Office (the "EPO"). The notice asserted, as applicable, the '190 patent is contrary to the provision of Article 123(2) EPC, Article 75(1) EPC and Article 100(c) EPC, and alleges the '190 patent lacks novelty and/or is obvious contrary to the provisions of Articles 54 and/or 56 EPC, and Article 100(a) EPC, and that the specification of the '190 patent does not provide sufficient disclosure of the subject matter of the inventions contravening Article 83 EPC and Article 100(b). On January 17, 2023, the Company timely filed a response before the European Opposition Division of the EPO contesting each of these assertions, with further oral proceedings scheduled to follow on January 18, 2024. On June 2, 2023, the European Opposition Division issued a non-binding preliminary decision. On January 18, 2024, the European Opposition Division held oral proceedings addressing each allegation of invalidity raised by Kymab and maintained the '190 patent as granted, and issued a written decision documenting these conclusions on February 16, 2024. Further proceedings may follow if appealed by Kymab before the Technical Board of Appeals. The Company does not expect significant impact on its assets or liabilities as a result of the opposition proceeding.

Prepaid Expenses and Other Assets (Tables)

12 Months Ended

Dec. 31, 2023

Prepaid Expense and Other Assets, Current [Abstract]

Schedule of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following:


	December 31,
	2023		2022
	(In thousands)
Prepaid research and development expenses	$	6,872	$	6,372
Prepaid general and administrative costs		2,058		2,940
Interest receivable		1,552		647
Other		1,527		2,204
Total	$	12,009	$	12,163

Employee Benefit Plans - Summary of Key Weighted Average Assumptions used in Pricing Model on date of Grant for Options Granted to Employees (Details) - Stock Option Activity	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	3.60%	2.00%	0.60%
Contractual life of options (years)	10 years	10 years	10 years
Expected term of options (years)	6 years 2 months 12 days	6 years 3 months 18 days	6 years 1 month 6 days
Expected volatility of underlying stock	68.30%	75.50%	85.70%
Expected dividend yield	0.00%	0.00%	0.00%

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Related Party Transactions

12 Months Ended

Dec. 31, 2023

Related Party Transactions

15. Related Party Transactions

The Company has entered into the Incyte collaboration and license agreement and the Incyte share subscription agreement in which the terms and transactional amounts incurred between Incyte and the Company are more fully described in Note 12. Incyte is a shareholder with holdings representing approximately 6.9%, 7.7% and 8.2% of the outstanding shares of the Company as of December 31, 2023, 2022 and 2021, respectively. During the year ended December 31, 2021, Incyte’s holdings of the Company’s outstanding shares fell below 10.0% of the Company’s total outstanding shares due to the Company issuing additional shares of common stocks through various financing events of 2021. These consolidated financial statements present Incyte as a related party for the year ended December 31, 2021 in order to simplify the presentation and clearly display transactional amounts incurred between Incyte and the Company, given the related party relationship in effect for a portion of the year. The consolidated financial statements for the years ended December 31, 2023 and 2022 do not reflect Incyte as a related party.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

8. Income Taxes

The components of loss from operations before income tax expense are as follows:


	Year ended December 31,
	2023			2022			2021
				(In thousands)
United States	$	(6,117	)	$	(10,437	)	$	(8,502	)
Netherlands		(145,630	)		(119,798	)		(58,075	)
Total loss before income taxes	$	(151,747	)	$	(130,235	)	$	(66,577	)

The components of income tax expense (benefit) from continuing operations are as follows:


	December 31,
	2023		2022			2021
	(In thousands)
U.S. federal	$	1,640	$	1,815		$	173
U.S. state		710		768			73
Total current tax expense	$	2,350	$	2,583		$	246

U.S. federal	$	595	$	(1,148	)	$	(5	)
U.S. state		247		(476	)		(2	)
Total deferred tax expense (benefit)	$	842	$	(1,624	)	$	(7	)

Total income tax expense	$	3,192	$	959		$	239

The Company recognizes income tax expense (benefit) based on its continuing operations in the U.S. The parent company in the Netherlands has net operating losses.

The parent company is subject to income tax in the Netherlands where a greater proportion of economic activity is attributed. A reconciliation of the Netherlands statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended December 31,
	2023			2022			2021
Netherlands statutory income tax rate		25.8	%		25.8	%		25.0	%
Changes in tax rates		—			—			5.2
Non-deductible expenses		(2.4	)		(4.4	)		0.7
Change in valuation allowance		(24.9	)		(22.0	)		(31.4	)
Other		(0.6	)		(0.1	)		0.1
Effective income tax rate		(2.1	)%		(0.7	)%		(0.4	)%

In 2020 and 2021, Dutch tax authorities enacted new tax rates applicable to future periods which impact the measurement of deferred income taxes. The effect of the change in the valuation allowance each year reflects the increase or decrease in the valuation allowance against deferred tax assets attributable to the Netherlands.

The components of the Company’s deferred tax assets (liabilities) consist of the following:


	December 31,
	2023			2022
	(In thousands)
Deferred tax assets:
Net operating loss carryforwards	$	161,966		$	110,722
Deferred revenue		10,903			17,593
Research and development costs		—			1,419
Excess interest carryforward		84			1,316
Lease obligation		3,160			3,507
Accrued expenses and other		1,238			696
Total deferred tax assets		177,351			135,253
Deferred tax asset valuation allowance		(173,152	)		(129,848	)
Total deferred tax assets, net of valuation allowance	$	4,199		$	5,405

Deferred tax liabilities:
Operating lease right-of-use assets	$	2,953		$	3,286
Other		47			79
Total deferred tax liabilities	$	3,000		$	3,365

Net deferred tax asset	$	1,199		$	2,041

After consideration of all positive and negative evidence, the Company believes that it is more-likely-than-not that our Netherlands deferred tax assets that are not supported by reversing temporary differences will not be realized. As a result, the Company established a valuation allowance of $173.2 million and $129.8 million as of December 31, 2023 and 2022, respectively. The increase in the valuation allowance of $43.3 million and $23.4 million for the years ended December 31, 2023 and 2022, respectively, is primarily attributable to the increase in net operating loss carryforward deferred tax assets for which a full valuation allowance applies. As of December 31, 2023, the portion of the valuation allowance for deferred tax assets for which subsequently recognized tax benefits would be credited directly to contributed capital totaled $5.4 million.

As of December 31, 2023, the Company did not have any net operating losses for U.S. federal or state income tax purposes. The Company had net operating loss carryforwards for Dutch income tax purposes of $628.0 million as of December 31, 2023. Under Dutch tax law, net operating loss carryforwards may be used to offset future taxable income in full up to €1.0 million and 50% of taxable income that exceeds €1.0 million. Effective as of January 1, 2022, these losses can be carried forward indefinitely.

As of December 31, 2023, the Company had no unrecognized tax benefits. As of December 31, 2023, the Company had no accrued interest or penalties related to underpayments of income taxes and no amounts have been recognized in the consolidated statements of operations. The Company will recognize interest and penalties related to an underpayment of income taxes in income tax expense.

The Company files income tax returns in the U.S. federal and Massachusetts jurisdictions as well as in the Netherlands. The statute of limitations for assessment by the Internal Revenue Service (IRS), and Massachusetts tax authorities is closed for tax years prior to 2020. The statute of limitations for assessment by the Netherlands tax authorities is closed for tax years prior to 2018. The Company is not currently under examination by the IRS or any other jurisdictions for any tax years.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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-Paragraph 1
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Investments in Debt Securities - Summary of Debt Securities by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	$ 231,715	$ 197,341
AAA [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	28,273
AA- to AA+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	81,593
A- to A+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	121,849
Money market funds [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	24,273	18,404
Money market funds [member] \| AAA [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	24,273
Money market funds [member] \| AA- to AA+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	0
Money market funds [member] \| A- to A+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	0
Corporate paper and notes [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	146,415	126,102
Corporate paper and notes [member] \| AAA [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	0
Corporate paper and notes [member] \| AA- to AA+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	33,526
Corporate paper and notes [member] \| A- to A+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	112,889
U.S. government agency securities [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	39,456	34,364
U.S. government agency securities [member] \| AAA [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	4,000
U.S. government agency securities [member] \| AA- to AA+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	27,482
U.S. government agency securities [member] \| A- to A+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	7,974
U.S. treasuries [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	21,571	$ 18,471
U.S. treasuries [member] \| AAA [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	0
U.S. treasuries [member] \| AA- to AA+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	20,585
U.S. treasuries [member] \| A- to A+ [member]
Debt Securities Held To Maturity Credit Quality Indicator [Line Items]
Balance	$ 986

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Public Offerings, Net of Underwriting Discounts and Commissions and Offering Cost [Member]	Lilly	Common Stock [Member]	Common Stock [Member] Public Offerings, Net of Underwriting Discounts and Commissions and Offering Cost [Member]	Common Stock [Member] Lilly	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Public Offerings, Net of Underwriting Discounts and Commissions and Offering Cost [Member]	Additional Paid-In Capital [Member] Lilly	Accumulated Deficit [Member]	Accumulated Deficit [Member] Public Offerings, Net of Underwriting Discounts and Commissions and Offering Cost [Member]	Accumulated Deficit [Member] Lilly	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Other Comprehensive (Loss) Income [Member] Public Offerings, Net of Underwriting Discounts and Commissions and Offering Cost [Member]	Accumulated Other Comprehensive (Loss) Income [Member] Lilly
Beginning balance at Dec. 31, 2020	$ 102,263			$ 3,211			$ 490,093			$ (400,112)			$ 9,071
Beginning balance, shares at Dec. 31, 2020				31,602,953
Issuance of common stock, net	248,058		$ 16,477	$ 1,072		$ 77	246,986		$ 16,400	0		$ 0	0		$ 0
Issuance of common stock,net, shares				10,014,354		706,834
Exercise of stock options and vesting of restricted stock units	17,423			$ 121			17,302			0			0
Exercise of stock options and vesting of restricted stock units, shares				1,142,911
Repurchase of restricted stock units	(285)			$ 0			(285)			0			0
Short-swing profit disgorgement	282			0			282			0			0
Share-based compensation	17,091			0			17,091
Currency translation adjustment	(18,292)			0			0			0			(18,292)
Net loss	(66,816)			0			0			(66,816)			0
Ending balance at Dec. 31, 2021	316,201			$ 4,481			787,869			(466,928)			(9,221)
Ending balance, shares at Dec. 31, 2021				43,467,052
Issuance of common stock, net		$ 57,527			$ 258			$ 57,269			$ 0			$ 0
Issuance of common stock,net, shares					2,720,846
Exercise of stock options and vesting of restricted stock units	1,213			$ 12			1,201			0			0
Exercise of stock options and vesting of restricted stock units, shares				122,691
Short-swing profit disgorgement	0
Share-based compensation	24,535			$ 0			24,535			0			0
Currency translation adjustment	(21,227)			0			0			0			(21,227)
Net loss	(131,194)			0			0			(131,194)			0
Ending balance at Dec. 31, 2022	247,055			$ 4,751			870,874			(598,122)			(30,448)
Ending balance, shares at Dec. 31, 2022				46,310,589
Issuance of common stock, net		$ 225,500			$ 1,093			$ 224,407			$ 0			$ 0
Issuance of common stock,net, shares					11,113,189
Exercise of stock options and vesting of restricted stock units	4,586			$ 39			4,547			0			0
Exercise of stock options and vesting of restricted stock units, shares				402,101
Short-swing profit disgorgement	0
Share-based compensation	26,226			$ 0			26,226			0			0
Currency translation adjustment	7,915			0			0			0			7,915
Net loss	(154,939)			0			0			(154,939)			0
Ending balance at Dec. 31, 2023	$ 356,343			$ 5,883			$ 1,126,054			$ (753,061)			$ (22,533)
Ending balance, shares at Dec. 31, 2023				57,825,879

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (154,939)	$ (131,194)	$ (66,816)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization of property and equipment	2,325	981	1,245
Amortization of intangible assets	215	304	240
Foreign exchange losses (gains)	13,951	(23,528)	(27,703)
Share-based compensation expense	26,226	24,535	17,091
Amortization (accretion) of discount on investments	(5,074)	(407)	450
Deferred tax benefit	842	(1,624)	(7)
Changes in operating assets and liabilities:
Accounts receivable	1,726	1,831	(4,991)
Operating lease right-of-use assets and lease obligations	(84)	815	(24)
Prepaid expenses and other current assets	2,648	(7,344)	(1,092)
Accounts payable	(3,931)	(3,920)	10,715
Accrued expenses and other liabilities	1,615	15,648	2,127
Deferred revenue	(27,727)	(25,996)	9,138
Net cash used in operating activities	(142,207)	(149,899)	(59,627)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(235,263)	(219,725)	(215,839)
Proceeds from maturities of marketable securities	212,225	230,166	70,086
Purchases of intangible assets	0	(52)	0
Purchases of property and equipment	(3,982)	(7,587)	(870)
Net cash provided by (used in) investing activities	(27,020)	2,802	(146,623)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payment of offering costs	(445)	(214)	(572)
Proceeds from issuance of common stock, net	225,945	57,740	248,630
Proceeds from stock options exercised	4,586	1,213	17,423
Repurchase of restricted stock units	0	0	(285)
Short-swing profit disgorgement	0	0	282
Net cash provided by financing activities	230,086	58,739	281,955
Foreign exchange impact on cash, cash equivalents and restricted cash	(4,284)	(4,952)	2,761
Net increase (decrease) in cash, cash equivalents and restricted cash	56,575	(93,310)	78,466
Cash, cash equivalents, and restricted cash, beginning of period	148,439	241,749	163,283
Cash, cash equivalents, and restricted cash, end of period	205,014	148,439	241,749
SUPPLEMENTAL DISCLOSURES:
Lease liabilities arising from obtaining right-of-use assets	0	11,493	2,626
Income taxes paid	3,103	0	(635)
Non-cash purchases of property, equipment and intangibles	42	2,093	0
Non-cash issuance of stock options	0	0	573
Income tax refunds received	0	0	0
CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Cash and cash equivalents	204,246	147,749	241,435
Restricted cash included in other assets	768	690	314
Cash, cash equivalents, and restricted cash, end of period	205,014	148,439	241,749
Lilly
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock - Lilly	$ 0	$ 0	$ 16,477

Income Taxes - Reconciliation of Netherlands Statutory Income Tax Rate and Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Netherlands statutory income tax rate	25.80%	25.80%	25.00%
Changes in tax rates	0.00%	0.00%	5.20%
Non-deductible expenses	(2.40%)	(4.40%)	0.70%
Change in valuation allowance	(24.90%)	(22.00%)	(31.40%)
Other	(0.60%)	(0.10%)	0.10%
Effective income tax rate	(2.10%)	(0.70%)	(0.40%)

CONSOLIDATED BALANCE SHEETS (Parenthetical) - € / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Common shares, par value	€ 0.09	€ 0.09
Common shares, authorized	67,500,000	67,500,000
Common shares, issued	57,825,879	46,310,589
Common shares, outstanding	57,825,879	46,310,589

Property and Equipment, net

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property and Equipment, net

5. Property and Equipment, net

Property and equipment, net consists of the following:


	December 31,
	2023			2022
	(In thousands)
Laboratory equipment	$	7,489		$	6,349
Office equipment and furniture		2,052			1,872
Leasehold improvements		10,293			9,111
Construction in progress		44			75
Property and equipment		19,878			17,407
Less: accumulated depreciation and amortization		(7,743	)		(5,185	)
Property and equipment, net	$	12,135		$	12,222

Construction in progress relates to certain ongoing development and construction costs related to the office lease the Company entered into with Kadans Science Partner XII B.V. that was entered into during 2022. Additional details for the lease agreement are described in Note 9 Operating Leases. Depreciation and amortization expense was $2.3 million, $1.0 million and $1.2 million for the years ended December 31, 2023, 2022 and 2021, respectively. Property and equipment are predominantly located in the Netherlands.

Employee Benefit Plans

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Employee Benefit Plans

13. Employee Benefit Plans

Share-Based Compensation

2010 Plan

In 2010, the Company established the Merus B.V. 2010 Employee Option Plan (the “2010 Plan”) that entitled key management personnel, staff and consultants providing similar services to purchase shares in the Company. Under the 2010 Plan, holders of vested options were entitled to purchase depositary receipts for common shares at the exercise price determined at the date of grant. Upon exercise of the option, common shares were issued to a foundation established to facilitate administration of share-based compensation awards and pool the voting interests of the underlying shares, and depositary receipts were issued by the foundation to the individual holders. In connection with the IPO, the 2010 Plan was amended to cancel the depositary receipts and allow individual holders to directly hold the common shares obtained upon exercise of their options.

Options granted under the 2010 Plan generally vest in installments over a four-year period from the grant date: 25% on the first anniversary of the vesting commencement date, and the remaining 75% of the options vest in 36 monthly installments for each full month of continuous service provided thereafter. Options expire after 8 years from the date of grant. The last grant of options pursuant to the 2010 Plan occurred in 2016, with no further grants awarded. All grants from the 2010 Plan were either exercised or terminated as of December 31, 2023.

2016 Plan

In 2016, the Company established the 2016 Incentive Award Plan (the “2016 Plan”). All incentive award grants since 2016 are being made under the 2016 Plan.

Options granted to employees under the 2016 Plan generally vest in installments over a four-year period from the grant date: 25% vest on the first anniversary of the vesting commencement date, and the remaining 75% of the options vest in 36 monthly installments for each full month of continuous service provided thereafter. Certain options may vest dependent on the attainment of performance criteria. Options expire after 10 years from the date of grant.

Options granted to non-executive directors consist of initial option grants as well as subsequent annual awards. The initial award of options granted vest in installments over a three-year period: 33% of the options vest on the first anniversary of the vesting commencement date, and 67% of the options vest in 24 monthly installments thereafter. Each subsequent award vests over a one-year period in 12 monthly installments. The Company measures the fair value of an option through the application of an option pricing model, as more fully described below.

The RSUs granted to employees under the 2016 Plan vest in installments over a four-year period from the grant date. Certain RSUs may vest dependent on the attainment of performance criteria. Each RSU represents the right to receive one common share. The fair value of an RSU is determined by reference to the price of the underlying common share.

The number of common shares authorized for issuance for future grants under the 2016 Plan as of January 1, 2024 totaled 2,005,113.

Share-Based Compensation Expense

Share-based compensation expense is classified in the consolidated statements of operations and comprehensive loss as follows:


	Year Ended December 31,
	2023		2022		2021
	(In thousands)
Research and development	$	11,593	$	10,658	$	7,167
General and administrative		14,633		13,877		9,924
Total	$	26,226	$	24,535	$	17,091

As of December 31, 2023, share-based compensation expense related to unvested shares was $19.1 million. These shares are expected to vest and related costs are expected to be recognized over a weighted average remaining vesting period of 1.3 years.

Stock Option Valuation

The Company uses the Black-Scholes option-pricing model to measure the fair value of stock option awards. Key weighted average assumptions used in this pricing model on the date of grant for options granted to employees are as follows:


	Year Ended December 31,
	2023			2022			2021
Risk-free interest rate		3.6	%		2.0	%		0.6	%
Contractual life of options (years)		10.0			10.0			10.0
Expected term of options (years)		6.2			6.3			6.1
Expected volatility of underlying stock		68.3	%		75.5	%		85.7	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

The risk-free interest rate is based upon the U.S. Treasury yield curve in effect at the time of grant, with a term that approximates the expected life of the option. Prior to April 1, 2022, the Company determined the expected volatility using a blended approach encompassing its historical experience and the historical volatility of a peer group of comparable publicly traded companies with product candidates in similar stages of development to the Company’s product candidates. From April 1, 2022 onward, the expected volatility is based on the annualized daily historical volatility of the Company's stock price for a time period consistent with the expected term of each grant. A simplified method using a weighted-average mid-point between an award’s vesting date and expiry is used to estimate the expected life of options in all periods presented as a sufficient history of participant exercise behavior is not readily observable. The Company has applied an expected dividend yield of 0.0% as the Company has not historically declared a dividend and does not anticipate declaring a dividend during the expected life of the options.

Stock Option Activity

The following is a summary of stock option activity for the year ended December 31, 2023:


	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(years)		(In thousands)
Outstanding at January 1, 2023		5,722,346		$	20.38
Granted		2,700,127			18.10
Exercised		(392,101	)		11.70
Forfeited or expired		(381,364	)		21.04
Outstanding at December 31, 2023		7,649,008		$	19.99		7.6	$	57,541
Exercisable at December 31, 2023		3,816,327		$	19.91		6.4	$	29,018


	Year Ended December 31,
	2023		2022
Weighted-average fair value of options granted	$	11.70	$	16.18

RSU Activity

The following is a summary of RSU activity for the year ended December 31, 2023:


	Number of RSUs			Weighted Average Grant-date Fair Value
Non-vested at January 1, 2023		25,000		$	21.87
Granted		20,000			21.20
Vested		(10,000	)		24.61
Forfeited		(15,000	)		20.04
Non-vested at December 31, 2023		20,000			21.20

Intrinsic Value of Stock Options Exercised and Vested RSUs


	Year Ended December 31,
	(In thousands)
	2023		2022
Total fair value of RSUs vested	$	238	$	423
Aggregate intrinsic value of options exercised		3,937		1,369

Post-Employment Benefit Plan

The Company has established a post-employment benefit plan for employees of the Netherlands that entitles executive officers and other staff members to retire at the age of 67 and receive annual payments based upon the average salary earned during the service period. The Company has insured the benefit liabilities through purchased non-participating annuities from an insurance company and has no other obligation other than to pay the annual insurance premiums to the insurance company. After purchasing the insurance, the Company has no further obligation (legal or constructive) to pay further amounts if the insurance fund has insufficient assets to pay all employee benefits relating to current and prior service. Contributions to purchase non-participating annuities are expensed as incurred as service costs. Company contributions to the post-employment benefit plan totaled $1.6 million, $2.8 million, and $2.9 million in the years ended December 31, 2023, 2022 and 2021, respectively.

401(k) Savings Plan

The Company has a defined contribution 401(k) savings plan (the “401(k) Plan”). The 401(k) Plan covers substantially all U.S. employees, and allows participants to defer a portion of their annual compensation on a pretax basis. The Company matches contributions to the 401(k) Plan, matching 50% of an employee’s contribution up to a maximum of 3% of the participant’s compensation. Company contributions to the 401(k) Plan totaled $0.3 million, $0.2 million, and $0.1 million for the years ended December 31, 2023, 2022, and 2021, respectively.

Executive Settlement

In December 2019, in connection with the departure of the Chief Executive Officer of the Company, the Company awarded benefits, including the following: cash compensation of $0.9 million, a grant of 30,000 RSUs, extended vesting of his equity incentive awards through June 30, 2021 and extended exercisability of his equity incentive awards through December 31, 2021. The cash compensation was paid by the Company in January 2020. There were no substantive service conditions associated with the benefits awarded other than the passage of time. The Company incrementally recognized $1.8 million in general and administrative expense associated with these benefits in the consolidated statement of operations for the year ended December 31, 2019.

In April 2020, Mark Throsby, Ph.D. resigned as the Executive Vice President and Chief Scientific Officer of the Company effective July 31, 2020. In connection with his departure, Mr. Throsby entered into a Settlement Agreement with the Company, pursuant to which Mr. Throsby received a severance payment equal to 8 months of his annual salary and amortized bonus aggregating approximately $0.3 million. Further, subject to Mr. Throsby’s continued compliance with the terms and conditions of the Settlement Agreement, Mr. Throsby’s unvested equity awards continued to vest until October 31, 2020 as if Mr. Throsby had continued in full time service with the Company through such date. The post-termination exercise period of Mr. Throsby's options was extended to March 31, 2021. The Company incrementally recognized $0.1 million in respect of the severance payment and a net reversal of $0.4 million of share-based compensation expense in respect of share-based compensation in research and development expense in the consolidated statement of operations in the prior year ended December 31, 2019.

In March 2021, the Company and Mr. Throsby amended the Settlement Agreement, extending the post-termination expiration period of his outstanding options to extend to October 31, 2021, three months following his performance of certain consulting services through July 31, 2021. As a result, additional compensation cost of $0.2 million was recognized for the quarter ended March 31, 2021. During the three months ended September 30, 2021, the Company and Mr. Throsby entered into the 2nd Amendment to the Settlement Agreement, extending Mr. Throsby’s consulting services period to November 30, 2021. The 2nd Amendment extends the post-termination expiration period of his outstanding options to February 28, 2022. As the modification occurred in Mr. Throsby’s post-employment period, the options cease to be within the scope of ASC 718 and are recharacterized as an issuance of a standalone derivative instrument. The Company recognized a $1.0 million net loss associated with the derivative instrument included as other losses, net in the statement of operations for the year ended December 31, 2021. The Company recognized a $0.4 million net gain associated with the derivative instrument included as other income in the statement of operations during the year ended December 31, 2022. The Company did not recognize any further gains or expenses during the year ended December 31, 2023 and the Company does not expect to incur any further expenses as Mr. Throsby's option to exercise expired in May 2022.

Employee Benefit Plans - Summary of Share-based Compensation Expense Classified in Consolidated Statements of Operations and Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total	$ 26,226	$ 24,535	$ 17,091
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total	11,593	10,658	7,167
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total	$ 14,633	$ 13,877	$ 9,924

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Feb. 22, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Registrant Name	MERUS N.V.
Trading Symbol	MRUS
Entity Central Index Key	0001651311
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding		57,878,284
Entity Public Float			$ 1,303.6
Entity File Number	001-37773
Entity Incorporation, State or Country Code	P7
Entity Tax Identification Number	00-0000000
Entity Address, Address Line One	Uppsalalaan 17
Entity Address, City or Town	Utrecht
Entity Address, Postal Zip Code	3584 CT
Entity Address, Country	NL
City Area Code	+31 30
Local Phone Number	253 8800
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common shares, nominal value €0.09 per share
Security Exchange Name	NASDAQ
Auditor Firm ID	1012
Auditor Name	KPMG Accountants N.V.
Auditor Location	Amstelveen, The Netherlands
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement that the registrant intends to file with the Securities and Exchange Commission pursuant to Regulation 14A in connection with the registrant’s 2024 Annual General Meeting of Shareholders are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.
Document Financial Statement Error Correction [Flag]	false

Collaborations - Additional Information (Details)				1 Months Ended			12 Months Ended
Collaborations - Additional Information (Details)	Jan. 18, 2021 USD ($) $ / shares shares	Mar. 14, 2018 EUR (€) Antibody	Jan. 23, 2017 USD ($)	Jan. 31, 2022	Jan. 31, 2018 USD ($) Antibody PerformanceObligation	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2023 EUR (€) Milestone	Dec. 31, 2023 USD ($) Milestone	Dec. 31, 2022 EUR (€) Milestone	Dec. 31, 2022 USD ($) Milestone	Dec. 31, 2021 USD ($) Milestone	Dec. 31, 2020 EUR (€)	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	Feb. 12, 2021 USD ($)	Dec. 10, 2018 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Net fair value of shares											$ 285,000
Development milestones recognized								$ 2,500,000
Research and development								140,658,000		$ 149,424,000	98,187,000
Lilly Collaborations Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment receivable	$ 40,000,000
Issuance of common stock,net, shares \| shares	706,834
Common stock stated purchase price per share \| $ / shares	$ 28.295
Proceeds from issuance of common stock, net	$ 20,000,000
Fixed consideration	43,500,000														$ 43,500,000
Fee incurred for extension of research term								500,000		500,000
Upfront payment	40,000,000
Net fair value of shares	$ 16,500,000
Incyte Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment receivable						$ 120,000,000
Issuance of common stock,net, shares \| shares						3,200,000
Common stock stated purchase price per share \| $ / shares						$ 25
Collaborations, transaction price as revenue						$ 80,000,000
Development milestones recognized								1,000,000		1,000,000	2,000,000
Additional development or commercialization milestones recognized								0
Incyte Collaboration and License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Residual royalty percentage				4.00%
Incyte Collaboration and License Agreement \| License and Related Activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborations, transaction price as revenue						$ 152,600,000
Collaborations, transaction price as deferred revenue			$ 152,600,000
Second ONO Research and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment receivable \| €		€ 700,000
Development milestones recognized										$ 1,000,000
Development milestones received \| €							€ 0		€ 1,000,000			€ 0
Payment to compensate research services \| €		300,000
Over time payment for full time equivalent funding \| €		€ 200,000
Second ONO Research and License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of bispecific antibodies under collaboration and license agreement \| Antibody		5
Simcere Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborations, transaction price as revenue					$ 2,750,000
Development milestones recognized								$ 0
Milestones achieved recognized											$ 500,000		$ 500,000
Number of milestones achieved \| Milestone							3	3
Non-refundable upfront payment received					$ 2,750,000
Milestone payments received								$ 1,800,000
Simcere Collaboration and License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of bispecific antibodies under collaboration and license agreement \| Antibody					3
Simcere Collaboration and License Agreement \| License and Performance \| Research and Development
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of performance obligation \| PerformanceObligation					3
Betta Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment receivable																$ 1,000,000
Development milestones received													2,000,000
Number of milestones achieved \| Milestone							0	0	0	0	0
Contingent milestone payments receivable																$ 12,000,000
Revenue related performance obligation as revenue														$ 1,000,000
Milestone revenue													2,000,000
Research and development													$ 2,000,000

Employee Benefit Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Number of Options, Outstanding, Beginning balance	5,722,346
Number of Options, Granted	2,700,127
Number of Options, Exercised	(392,101)
Number of Options, Forfeited or expired	(381,364)
Number of Options, Outstanding, Ending balance	7,649,008	5,722,346
Number of Options, Exercisable	3,816,327
Weighted Average Exercise Price per Share, Outstanding, Beginning balance	$ 20.38
Weighted Average Exercise Price per Share, Granted	18.10
Weighted Average Exercise Price per Share, Exercised	11.70
Weighted Average Exercise Price per Share, Forfeited or expired	21.04
Weighted Average Exercise Price per Share, Outstanding, Ending balance	19.99	$ 20.38
Weighted Average Exercise Price per Share, Exercisable	$ 19.91
Weighted Average Remaining Contractual Term, Outstanding	7 years 7 months 6 days
Weighted Average Remaining Contractual Term, Exercisable	6 years 4 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 57,541
Aggregate Intrinsic Value, Exercisable	$ 29,018
Weighted-average fair value of options granted	$ 11.70	$ 16.18

Prepaid Expenses and Other Assets - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid research and development expenses	$ 6,872	$ 6,372
Prepaid general and administrative costs	2,058	2,940
Interest receivable	1,552	647
Other	1,527	2,204
Total	$ 12,009	$ 12,163

Accrued Expenses and Other Liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Summary of Accrued Expenses

Accrued expenses consisted of the following:


	December 31,
	2023		2022
	(In thousands)
Accrued research and development expenses	$	27,970	$	26,159
Accrued personnel costs		8,348		5,778
Accrued general and administrative expenses		2,129		3,615
Other		35		38
Accrued expenses	$	38,482	$	35,590

Investments in Debt Securities - Summary of Classification of Debt Securities in Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities Held To Maturity Nonaccrual [Line Items]
Balance	$ 231,715	$ 197,341
Cash equivalents [member]
Debt Securities Held To Maturity Nonaccrual [Line Items]
Balance	24,273	18,404
Current marketable securities [member]
Debt Securities Held To Maturity Nonaccrual [Line Items]
Balance	150,130	142,480
Non-current marketable securities [member]
Debt Securities Held To Maturity Nonaccrual [Line Items]
Balance	$ 57,312	$ 36,457

Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and Equipment, gross	$ 19,878	$ 17,407
Less: accumulated depreciation and amortization	(7,743)	(5,185)
Property and equipment, net	12,135	12,222
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and Equipment, gross	7,489	6,349
Office Equipment and Furniture
Property Plant And Equipment [Line Items]
Property and Equipment, gross	2,052	1,872
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and Equipment, gross	10,293	9,111
Construction in Progress
Property Plant And Equipment [Line Items]
Property and Equipment, gross	$ 44	$ 75

Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Summary of Share-based Compensation Expense Classified in Consolidated Statements of Operations and Comprehensive Loss

Share-based compensation expense is classified in the consolidated statements of operations and comprehensive loss as follows:


	Year Ended December 31,
	2023		2022		2021
	(In thousands)
Research and development	$	11,593	$	10,658	$	7,167
General and administrative		14,633		13,877		9,924
Total	$	26,226	$	24,535	$	17,091

Summary of Key Weighted Average Assumptions Used in Pricing Model on Date of Grant for Options Granted to Employees


	Year Ended December 31,
	2023			2022			2021
Risk-free interest rate		3.6	%		2.0	%		0.6	%
Contractual life of options (years)		10.0			10.0			10.0
Expected term of options (years)		6.2			6.3			6.1
Expected volatility of underlying stock		68.3	%		75.5	%		85.7	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

Summary of Stock Option Activity

The following is a summary of stock option activity for the year ended December 31, 2023:


	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(years)		(In thousands)
Outstanding at January 1, 2023		5,722,346		$	20.38
Granted		2,700,127			18.10
Exercised		(392,101	)		11.70
Forfeited or expired		(381,364	)		21.04
Outstanding at December 31, 2023		7,649,008		$	19.99		7.6	$	57,541
Exercisable at December 31, 2023		3,816,327		$	19.91		6.4	$	29,018


	Year Ended December 31,
	2023		2022
Weighted-average fair value of options granted	$	11.70	$	16.18

Summary of RSU Activity

The following is a summary of RSU activity for the year ended December 31, 2023:


	Number of RSUs			Weighted Average Grant-date Fair Value
Non-vested at January 1, 2023		25,000		$	21.87
Granted		20,000			21.20
Vested		(10,000	)		24.61
Forfeited		(15,000	)		20.04
Non-vested at December 31, 2023		20,000			21.20

Intrinsic Value of Stock Options Exercised and Vested RSUs


	Year Ended December 31,
	(In thousands)
	2023		2022
Total fair value of RSUs vested	$	238	$	423
Aggregate intrinsic value of options exercised		3,937		1,369

Intangible Assets, Net - Summary of Intangible Assets, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 3,749	$ 3,692
Less: accumulated amortization	(1,949)	(1,742)
Intangible assets, net	1,800	1,950
Licenses of Intellectual Property [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	3,565	3,441
Software Licenses [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 184	$ 251

Operating Leases - Schedule of Maturities of Operating Lease Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2021
Lease, Cost [Abstract]
2024	$ 2,208
2025	2,224
2026	1,785
2027	1,563
2028	1,563
Thereafter	5,100
Total lease payments	14,443	$ 100
Less: amount representing interest	(2,281)
Total lease obligations	$ 12,162

Operating Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Operating Leases

9. Operating Leases

The Company has noncancelable operating leases for offices and lab spaces expiring at various dates through 2032.

Merus N.V. has non-cancellable operating leases for its corporate headquarters in Utrecht, the Netherlands. In December 2022, the Company moved into its new headquarters called the "Accelerator" in the Utrecht Science Park, at 17 Uppsalalaan, 3rd and 4th floor, 3583 CT, Utrecht.

On July 19, 2019, Merus N.V. entered into a lease agreement with Kadans Science Partner XIII B.V. (“Kadans”) for the Accelerator headquarters. In April 2022, the Accelerator lease between the Company and Kadans commenced. In accordance with the accounting requirements under ASC 842, the right-of-use asset and lease obligation were not recorded until the lease commenced. In December 2022, the Company completed the fit-out construction on approximately 4,957 square meters of office and laboratory space in the premises. The lease provides for a base rent of approximately €1.4 million per annum. The rent amount is subject to adjustment based on the consumer price index (the “CPI”) annually, beginning one year after the lease commencement date, subject to certain limitations if the CPI is greater than 3.0%. The initial term of the lease is ten years with two 5-year renewal options following the initial term, unless earlier terminated by the Company or Kadans, except that the earliest Kadans may terminate the lease is 20 years from the completion date of the premise construction. The Company expects the lease to end as of April 4, 2032. On April 5, 2022, the Company recognized a right-of-use asset of $11.5 million, or €10.5 million, and a lease liability of $12.4 million, or €11.3 million, on the consolidated balance sheets. In connection with signing the lease, the Company received a lease incentive of $0.9 million, or €0.8 million. To measure the lease liability at the commencement date, the Company discounted the outstanding lease payments using an incremental borrowing rate of 4.85%. During the three months ended June 30, 2023, in accordance with the terms of the lease agreement, the annual rent for the Accelerator lease increased due to increases in the consumer price index (CPI). The portion of the rent payments related to the CPI index are included within variable lease costs. There have been no other changes in the Company’s lease arrangements during the twelve months ended December 31, 2023.

During the year ended December 31, 2021, the Company signed a lease amendment (the “Amendment”), which extended the term of the lease for its former corporate headquarters with Stichting Incubator Utrecht by approximately 1.5 years ending at the end of March 2023. The Amendment did not include additional right-of-use other than the extended lease term. There is no additional renewal term included in the Amendment to consider in the estimate of the lease term. On December 7, 2022, the Company signed a second lease amendment terminating the lease for the former corporate headquarters as of January 1, 2023. The Company continued to make payments through mid-February 2023. The Company accounted for the second amendment as a lease modification and reduced the lease liability and right-of-use asset by approximately $0.1 million to equal to the remaining lease payments. The lease liability and right-of-use asset for the former corporate headquarters was reduced to $0 as the final payments were made during the first quarter of 2023.

In March 2019, Merus US, Inc. entered into a non-cancellable operating lease agreement for office space in Cambridge, Massachusetts. The lease commenced in the second quarter of 2019 and has a term of seven years, and may be extended for another five years. Given the Company’s current plans, the renewal term has not been included in the estimate of the lease term. Fixed lease payments increase annually and include an increase on an inflationary measure. Variable payments include amounts due to the lessor for additional services and cost reimbursements.

The components of lease cost recorded in the Company’s consolidated statement of operations and statement of cash flows were as follows:


	For the Year Ended December 31,
	2023		2022
	(In thousands)
Operating lease cost	$	2,256	$	2,524
Variable lease cost		190		366
Total lease cost included in operating expenses	$	2,446	$	2,890

Cash paid to lessors included in operating cash outflows	$	2,367	$	2,622

The Company’s non-lease cost and other costs paid to the lessor are primarily related to services provided by the lessor in operating the premises that includes fees, operating costs, taxes and insurance related to the leased premises.

Maturities of the Company’s operating lease obligations as of December 31, 2023 were as follows (in thousands):


Year	Operating Leases
2024	$	2,208
2025	$	2,224
2026	$	1,785
2027	$	1,563
2028	$	1,563
Thereafter	$	5,100
Total lease payments	$	14,443
Less: amount representing interest	$	(2,281	)
Total lease obligations	$	12,162

The weighted-average remaining lease terms and discount rates related to the Company’s leases were as follows:


	As of December 31,
	2023			2022
Weighted-average remaining operating lease term (in years)		7.6			8.3
Weighted-average discount rate for operating leases		4.8	%		4.8	%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Summary of Components of Loss from Operations Before Income Tax Expense

The components of loss from operations before income tax expense are as follows:


	Year ended December 31,
	2023			2022			2021
				(In thousands)
United States	$	(6,117	)	$	(10,437	)	$	(8,502	)
Netherlands		(145,630	)		(119,798	)		(58,075	)
Total loss before income taxes	$	(151,747	)	$	(130,235	)	$	(66,577	)

Summary of Components of Expense for (Benefit) from Income Taxes

The components of income tax expense (benefit) from continuing operations are as follows:


	December 31,
	2023		2022			2021
	(In thousands)
U.S. federal	$	1,640	$	1,815		$	173
U.S. state		710		768			73
Total current tax expense	$	2,350	$	2,583		$	246

U.S. federal	$	595	$	(1,148	)	$	(5	)
U.S. state		247		(476	)		(2	)
Total deferred tax expense (benefit)	$	842	$	(1,624	)	$	(7	)

Total income tax expense	$	3,192	$	959		$	239

Reconciliation of Netherlands Statutory Income Tax Rate and Effective Income Tax Rate


	Year Ended December 31,
	2023			2022			2021
Netherlands statutory income tax rate		25.8	%		25.8	%		25.0	%
Changes in tax rates		—			—			5.2
Non-deductible expenses		(2.4	)		(4.4	)		0.7
Change in valuation allowance		(24.9	)		(22.0	)		(31.4	)
Other		(0.6	)		(0.1	)		0.1
Effective income tax rate		(2.1	)%		(0.7	)%		(0.4	)%

Summary of Components of Deferred Tax Assets (Liabilities)

The components of the Company’s deferred tax assets (liabilities) consist of the following:


	December 31,
	2023			2022
	(In thousands)
Deferred tax assets:
Net operating loss carryforwards	$	161,966		$	110,722
Deferred revenue		10,903			17,593
Research and development costs		—			1,419
Excess interest carryforward		84			1,316
Lease obligation		3,160			3,507
Accrued expenses and other		1,238			696
Total deferred tax assets		177,351			135,253
Deferred tax asset valuation allowance		(173,152	)		(129,848	)
Total deferred tax assets, net of valuation allowance	$	4,199		$	5,405

Deferred tax liabilities:
Operating lease right-of-use assets	$	2,953		$	3,286
Other		47			79
Total deferred tax liabilities	$	3,000		$	3,365

Net deferred tax asset	$	1,199		$	2,041

Income Taxes - Additional Information (Details) € in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 EUR (€)
Income Tax Disclosure [Line Items]
Deferred tax asset valuation allowance	$ 173,152,000	$ 129,848,000
Increase in valuation allowance, attributable to increase in net operating loss carryforward deferred tax assets	43,300,000	$ 23,400,000
Deferred tax asset valuation allowance	5,400,000
Unrecognized tax benefits	0
Accrued interest or penalties related to uncertain tax positions	0
Unrecognized tax benefits, tax related penalties and interest expense	0
Dutch Tax Law
Income Tax Disclosure [Line Items]
Operating Loss Carryforwards	$ 628,000,000
Taxable income that exceeds €1.0 million, percentage			50.00%
Dutch Tax Law \| Maximum
Income Tax Disclosure [Line Items]
Future taxable income offset limit \| €			€ 1.0
Dutch Tax Law \| Minimum
Income Tax Disclosure [Line Items]
Future taxable income exceeding limit \| €			€ 1.0

Intangible Assets, Net

12 Months Ended

Dec. 31, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Intangible Assets, Net

6. Intangible assets, net

Intangible assets, net consists of the following:


	December 31,
	2023			2022
	(In thousands)
Licenses of intellectual property	$	3,565		$	3,441
Software licenses		184			251
Intangible assets		3,749			3,692
Less: accumulated amortization		(1,949	)		(1,742	)
Intangible assets, net	$	1,800		$	1,950

Amortization expense was $0.2 million, $0.3 million, and $0.2 million for the years ended December 31, 2023, 2022 and 2021, respectively. Intangible assets are predominantly located in the Netherlands.

Amortization expense over the next five years is expected to be as follows (in thousands):


Year	Expected amortization
2024	$	164
2025		150
2026		150
2027		150
2028		150
Thereafter		1,036
Total remaining value	$	1,800

Related Party Transactions - Additional Information (Details) - Incyte - Merus N V [Member]	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Ownership percentage	6.90%	7.70%	8.20%
Maximum
Related Party Transaction [Line Items]
Ownership percentage	10.00%

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Estimated Useful Lives of Property and Equipment

The Company records property and equipment at cost. The Company calculates depreciation and amortization using the straight-line method over the following estimated useful lives:


Asset Category		Useful Lives
Laboratory equipment		5 years
Office furniture and equipment		5 years
Leasehold improvements		Shorter of term of lease or 10 years

Operating Leases - Summary of Components of Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Lease, Cost [Abstract]
Operating lease cost	$ 2,256	$ 2,524
Variable lease cost	190	366
Total lease cost included in operating expenses	2,446	2,890
Cash paid to lessors included in operating cash outflows	$ 2,367	$ 2,622

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Accounting Policies [Abstract]
Cash and cash equivalents, maturities	three months or less
Impairment charges of long-lived assets	$ 0	$ 0	$ 0
Reduction in research and development expenses	$ 6,300,000	$ 5,900,000	$ 9,300,000
Number of reportable segment \| Segment	1

Prepaid Expenses and Other Assets - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Other Assets
Restricted cash held on account as collateral	$ 0.8	$ 0.7

Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Property and Equipment (Details)	Dec. 31, 2023
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	5 years
Office Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful life	5 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	us-gaap:UsefulLifeTermOfLeaseMember

Employee Benefit Plans - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 30, 2020	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2019	Jan. 01, 2024
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Severance payment						$ 100,000
Additional compensation cost		$ 200,000
Net loss associated with the derivative instrument				$ 400,000	$ 1,000,000
Derivative, Gain on Derivative			$ 0
Derivative, Loss, Statement of Income or Comprehensive Income [Extensible Enumeration]					Nonoperating Income (Expense)
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Net reversal of stock-based compensation expense						400,000
401 (K) Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Defined contribution plan , description			The 401(k) Plan covers substantially all U.S. employees, and allows participants to defer a portion of their annual compensation on a pretax basis. The Company matches contributions to the 401(k) Plan, matching 50% of an employee’s contribution up to a maximum of 3% of the participant’s compensation.
Percentage of employer matching contribution				50.00%
Defined contribution plan, cost			$ 300,000	$ 200,000	$ 100,000
401 (K) Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Employer matching contribution, percent of employees compensation				3.00%
Postemployment Retirement Benefits
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contributions to post-employment benefit plan			1,600,000	$ 2,800,000	$ 2,900,000
Executive settlement, cash compensation to be paid						900,000
Executive settlement expense						$ 1,800,000
Executive settlements, cash compensation paid	$ 300,000
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation			$ 19,100,000
Weighted average remaining vesting period			1 year 3 months 18 days
Expected dividend yield			0.00%	0.00%	0.00%
Share-Based Payments
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield			0.00%
Share-Based Payments \| 2010 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options granted share-based payments			4 years
Options expiration period			8 years
Share-Based Payments \| 2010 Plan \| First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting rights, percentage			25.00%
Share-Based Payments \| 2010 Plan \| Thereafter
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting rights, percentage			75.00%
Award vesting rights, required service period			36 months
Share-Based Payments \| 2016 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options granted share-based payments			4 years
Options expiration period			10 years
Share-Based Payments \| 2016 Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares authorized for issuance for future grants							2,005,113
Share-Based Payments \| 2016 Plan \| Non-Executive Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options granted share-based payments			3 years
Share-Based Payments \| 2016 Plan \| Non-Executive Directors \| Subsequent Award
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of options granted share-based payments			1 year
Award vesting rights, required service period			12 months
Share-Based Payments \| 2016 Plan \| First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting rights, percentage			25.00%
Share-Based Payments \| 2016 Plan \| First Anniversary \| Non-Executive Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting rights, percentage			33.00%
Share-Based Payments \| 2016 Plan \| Thereafter
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting rights, percentage			75.00%
Award vesting rights, required service period			36 months
Share-Based Payments \| 2016 Plan \| Thereafter \| Non-Executive Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting rights, percentage			67.00%	67.00%
Award vesting rights, required service period			24 months	24 months
RSUs \| Postemployment Retirement Benefits
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant of RSUs						30,000
RSUs \| 2016 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Description of RSUs granted to employees			Each RSU represents the right to receive one common share.
Vesting period of RSUs granted share-based payments			4 years

Prepaid Expenses and Other Assets

12 Months Ended

Dec. 31, 2023

Prepaid Expense and Other Assets, Current [Abstract]

Prepaid Expenses and Other Assets

4. Prepaid Expenses and Other Assets

Prepaid expenses and other current assets consisted of the following:


	December 31,
	2023		2022
	(In thousands)
Prepaid research and development expenses	$	6,872	$	6,372
Prepaid general and administrative costs		2,058		2,940
Interest receivable		1,552		647
Other		1,527		2,204
Total	$	12,009	$	12,163

Restricted cash included in other assets totaled $0.8 million and $0.7 million as of December 31, 2023 and 2022, respectively. The nature of the restriction relates to amounts held as bank guarantees and collateral for a credit card borrowing arrangement.

Collaborations

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Collaborations

12. Collaborations

Lilly

On January 18, 2021, Eli Lilly and Company (“Lilly”) agreed to pay the Company a $40.0 million, non-refundable upfront payment, and purchased 706,834 common shares at a stated price per share of $28.295, for an aggregate purchase price of $20.0 million. The Company and Lilly agreed to collaborate with respect to the discovery and research of bispecific antibodies utilizing the Company’s proprietary Biclonics® bispecific technology platform. The collaboration encompasses up to three (3) independent programs directed to the generation of T-cell re-directing bispecific antibodies that bind CD3 and a tumor associated antigen target selected by Lilly to be the subject of each program.

The objective of each program is to develop a lead compound that Lilly would be able to continue to develop through clinical trials. Lilly agreed to fund the research activities the Company conducts for each program under an agreed research plan and budget. Lilly receives an exclusive, worldwide, royalty-bearing, sublicensable license, under certain patent rights and know-how to exploit certain compounds and products directed to designated targets in combination with targeting CD3, or directed to such designated target(s) alone as a monospecific antibody or monospecific antibody drug conjugate, subject to rights granted by Merus to third parties under one or more existing third party agreements. Merus retains all rights not granted to Lilly. Lilly has certain rights to replace selected targets, including the right to substitute a target selection after initial selection for a period of time. The Company may be entitled to further milestones and royalties in the future dependent on development and commercialization of any resulting product.

The initial term of the arrangement includes a three-year research term for the Company to perform research and development activities, subject to two extension terms of six months at Lilly’s discretion. While the arrangement may be terminated in its entirety or on a program-by-program basis at will by Lilly, there are no direct costs or penalties to Lilly to terminate the arrangement prior to the end of the initial term.

At inception of the arrangement, the Company identified a single performance obligation comprised of a combined delivery of a license and related activities, including research activities associated with a product candidate against the first target and the activities of the joint steering committee. The Company also identified two other combined performance obligations relating to options exercisable by Lilly to select a second and third target to advance a second and third product candidate against the selected targets through discovery and research.

The transaction price at inception was comprised of fixed consideration of $43.5 million that was derived from the $40.0 million upfront payment and $20.0 million share purchase proceeds, net of the fair value of shares of the shares delivered to Lilly of $16.5 million, and variable consideration associated with the funding of research services for the product candidate against the first target at inception. All other consideration under the arrangement was determined to be variable consideration and fully constrained at inception.

The fixed consideration was allocated equally amongst the three performance obligations and the variable consideration associated with each target was allocated to the performance obligation of each respective target. The equal allocation of the fixed consideration was based on the estimated standalone selling price of each performance obligation as each was materially the same.

On February 12, 2021, the Company and Lilly completed the initial exchange of fixed consideration and transfer of common shares. The Company initially deferred $43.5 million allocated to the performance obligations to be recognized as revenue over time using a cost-to-cost measure of progress toward the development of a lead compound for each respective target, anticipated to be recognized as revenue within the initial research term, along with research funding. Development milestones, commercialization milestones and royalties are variable consideration, fully constrained, to be included in the transaction price for each performance obligation and recognized in future periods in accordance with the Company’s revenue recognition policy. The revenue recognized relating to each combined performance obligation is presented in the notes according to the source of consideration received (upfront, reimbursement revenue, milestone), reflective of their differing timing of receipt.

During the year ended December 31, 2022, Lilly substituted one of the target programs. The program timeline is expected to extend beyond the original research term. Under the current research plan, for the program to be completed in collaboration with Merus, Lilly would be required to extend the research term to 2025, subject to its discretion. Lilly exercised the first six month extension in October 2023 for which there was no associated fee. The program timeline is expected to extend beyond this first extension, and such an extension into 2025 would result in a fee of $0.5 million. The $0.5 million extension is included in the Lilly cost-to-cost model as of December 31, 2023 and December 31, 2022.

As of December 31, 2023, research activities were on-going and no milestones have been achieved to date.

Incyte

In December 2016, pending regulatory clearance, Incyte Corporation (“Incyte”) agreed to pay the Company a $120.0 million, non-refundable upfront payment, and purchased 3.2 million common shares at a stated price per share of $25.00, for an aggregate purchase price of $80.0 million. In exchange, the Company granted Incyte with a license to certain of its intellectual property and committed to collaborate with Incyte to research, discover and develop monospecific or bispecific antibodies utilizing the Company’s proprietary bispecific technology platform. The collaboration is managed by a joint steering committee in which both parties are represented and is tasked with overseeing the activities which significantly contributes to the collaboration. The collaboration may encompass up to 10 product candidates that result from the Company’s application of its proprietary Biclonics® technology platform. During the course of the initial research term, Merus proposes product candidates to Incyte, which evaluates whether to designate proposed product candidates from the Company to make a selection for further research. Proposed product candidates begin at a pre-clinical stage of development. Incyte has certain rights to replace product candidates, including the right to substitute a product candidate after initial selection. The Company would be entitled to future consideration in the form of cost reimbursements for research services, development milestones, commercialization milestones and royalties related to the programs under the arrangement.

At inception of the collaboration, two potential bispecific product candidates were under preliminary evaluation. After further research, a lead candidate was ultimately selected for the first product candidate, designated MCLA-145, and the other potential product candidate was not pursued. For the designated product candidate (MCLA-145), the Company retained the exclusive right to develop and commercialize products and product candidates in the United States, while Incyte obtained the exclusive right to develop and commercialize products and product candidates arising from such program outside the United States. For MCLA-145, the parties will conduct and share equally the costs of mutually agreed global development activities and will be solely responsible for independent development activities in each party’s respective territories. For all other programs under the arrangement to be selected by Incyte, Incyte will be responsible for all research, development and commercialization costs. The Company may elect to co-fund the development of certain of the other programs in the future, in which case costs and benefits would be shared. The Company has not elected to co-fund any programs to date.

At inception of the arrangement, the Company identified a performance obligation comprised of a combined delivery of a license and related activities, including the activities of the joint steering committee, to which to allocate consideration. The arrangement also allowed for optional future research services to advance selected product candidates through discovery and research. The transaction price was comprised of fixed consideration of an upfront payment of $120.0 million and proceeds from the sale of shares of $80.0 million. All other consideration under the arrangement was determined to be variable consideration and fully constrained at inception. $152.6 million of the transaction price was allocated to the license and related activities performance obligation after accounting for the purchase of common shares by Incyte.

On January 23, 2017, the Company completed the sale of shares and exchange of the license. The Company initially deferred $152.6 million of the transaction price allocated to the license and related performance obligation as deferred revenue, to be recognized as revenue over time as the primary benefit of the license to Incyte is access to the Company’s intellectual property covering its Biclonics® technology platform for the generation of potential product candidates. Development milestones, commercialization milestones and royalties are variable consideration, fully constrained, to be recognized in future periods in accordance with the Company’s revenue recognition policy. Cost reimbursements for research services are recognized as they are performed over time as these are considered a separate performance obligation.

In January 2022, the Company announced that Incyte elected to opt-out of its ex-U.S. development of MCLA-145, from the parties joint collaboration agreement executed in 2017. At inception of the collaboration, for the designated product candidate (MCLA-145), the Company retained the exclusive right to develop and commercialize products and product candidates in the United States, while Incyte obtained the exclusive right to develop and commercialize products and product candidates arising from such program outside the United States. For MCLA-145, the parties conducted and shared equally the costs of mutually agreed global development activities. Incyte’s opt-out of ex-U.S. rights to MCLA-145 provides the Company the exclusive right to develop and commercialize potential MCLA-145 products globally. Under the collaboration, Incyte will continue to support the program for a limited time while ex-U.S. activities are transitioned to the Company, and Incyte will retain a right to a residual royalty of up to 4% on sales of future commercialization of MCLA-145, if approved.

During the year ended December 31, 2023, the Company recognized a $2.5 million milestone from Incyte related to the initiation of a Phase 1 study with respect to a novel target pair program, a second $2.5 million milestone from Incyte related to the initiation of a Phase 1 study with respect to a novel target pair program, and a $1.0 million milestone from Incyte related to candidate nomination. There were no additional development or commercialization milestones recognized during the year ended December 31, 2023. During the year ended December 31, 2022, the Company recognized a total of $1.0 million in development milestones. During the year ended December 31, 2021, the Company recognized a total of $2.0 million in development milestones.

Ono

In April 2014, the Company granted Ono Pharmaceutical Co., Ltd. (“Ono”) an exclusive, worldwide, royalty-bearing license, with the right to sublicense, research, test, make, use and market a limited number of bispecific antibody candidates based on the Company’s Biclonics® technology platform against two undisclosed targets directed to a particular undisclosed target combination.

On March 14, 2018, the Company granted Ono an exclusive, worldwide, royalty-bearing license, with the right to sublicense, research, test, make, use and market a limited number of bispecific antibody candidates based on the Company’s Biclonics® technology platform against two undisclosed targets directed to a particular undisclosed target combination. Ono is responsible for identifying lead candidates and conducting further non-clinical and clinical development activities for such licensed bispecific antibodies and pharmaceutical products containing such antibodies, including manufacture and process development. Additionally, Ono controls and has exclusive rights over the worldwide commercialization of any approved products, including worldwide supply, and is solely responsible for all costs and expenses related to commercialization. Ono has also agreed to fund the Company’s research and development activities and be responsible for the payment of all costs and expenses for its own research and development activities, which are set out in a mutually agreed upon research plan. The Company retains all rights to use and commercialize any antibodies that are generated under the collaborative research program, excluding the up to five lead and/or selected antibodies against the targets Ono is pursuing, provided that the use and commercialization is not with respect to the particular target combination. Ono agreed to pay the Company an upfront, non-refundable payment of €0.7 million. In addition, the Company was entitled to €0.3 million intended to compensate the Company for research services already completed upon entering into the agreement, and €0.2 million to be paid to the Company over time for full time equivalent funding. The Company is entitled to research and development milestones in addition to royalties on future sales. The Company identified performance obligations for: (1) provision of a license for the target combination, and (2) research and development services. The Company concluded that Ono would be able to develop and benefit from the license, independent of the research and development services. The research and development services are capable of being performed by third parties with an appropriate sub-license, and are recognized over time as these services are delivered. Milestone payments are fully constrained as variable consideration to be recognized in future periods in accordance with the Company’s revenue recognition policy.

There were no development milestones achieved in the year ended December 31, 2023. The Company achieved a €1.0 million (approximately $1.0 million) development milestone in the year ended December 31, 2022. There were no development milestones achieved in the year ended December 31, 2020.

Simcere

In January 2018, the Company granted Simcere Pharmaceuticals Group (“Simcere”) an exclusive license to develop and commercialize up to three bispecific antibodies to be produced by Merus utilizing the Company’s Biclonics® technology platform in China (the “Simcere Agreement”). The Company will retain all rights outside of China. The Company has agreed to lead research and discovery activities, while Simcere has agreed to be responsible for the Investigational New Drug (“IND”) enabling studies, clinical development, regulatory filings and commercialization of these potential product candidates in China. The Company received an upfront, non-refundable payment of $2.75 million, relating to three separate research programs.

At inception of the arrangement, the Company identified three performance obligations comprised of the combined delivery of a license and performance of research and development activities with respect to each program. The Company performs research and development activities to achieve candidate nomination. The Company concluded that these activities were not distinct from the underlying license for each program as Simcere would not be able to benefit from the license apart from research and development activities at this phase of development.

The transaction price under the arrangement comprised fixed consideration of $2.75 million. The transaction price was allocated to each separate performance obligation on a relative standalone fair value basis. The Company deferred the portion of the upfront payment allocated to the three performance obligations as deferred revenue, to be recognized over time. Compensation for research and development services prior to candidate nomination are allocated to each program performance obligation and also recognized over time. Development milestone payments allocated to each of the program performance obligations are constrained as variable consideration to be recognized in future periods in accordance with the Company’s revenue recognition policy.

The Company has achieved three milestones under this agreement and has received an aggregate of $1.8 million in milestone payments. During the years ended December 31, 2021 and 2020, the Company recognized $0.5 million for milestones achieved under the Simcere Agreement, respectively. In January 2022, the Company and Simcere terminated the Simcere Agreement, effective March 30, 2022. There were no milestones achieved during the year ended December 31, 2023.

Betta

On December 10, 2018, the Company granted Betta an exclusive license to develop and commercialize in China MCLA-129, proprietary Biclonics® produced by its Biclonics® technology platform. The Company retains all rights outside of China. Betta has agreed to retain a contract manufacturing organization with experience in filing IND applications with U.S. regulatory authorities and CTAs with European regulatory authorities in order to produce clinical trial materials for the Chinese market and rest of the world. As a key strategic component of the collaboration, Betta will be responsible for IND enabling studies and manufacturing of clinical trial materials in China, which the Company intends to use to assist regulatory filing and early stage clinical development in the rest of the world.

In addition to a non-refundable upfront payment of $1.0 million, Betta and the Company will share equally the cost of the transfer of the manufacturing technology to a contract manufacturing organization. The Company is also eligible to receive an aggregate of $12.0 million in milestone payments contingent upon Betta achieving certain specified development and commercial goals as well as tiered royalty payments of net sales of any products resulting from the collaboration in China. In turn, Betta is also entitled to milestone payments based on the Company’s progress.

The Company identified a single combined performance obligation, being the delivery of the MCLA-129 license including activities necessary to complete the technology transfer. The Company had no other commitments. The transaction price is comprised of fixed consideration of $1.0 million and fully allocated to the single performance obligation which would be fulfilled at a point in time. The technology transfer to deliver the license was completed in 2018 and Company recognized the revenue related to this performance obligation of $1.0 million as revenue for the year ended December 31, 2018. Development milestone payments allocated to the performance obligation are constrained as variable consideration to be recognized in future periods in accordance with the Company’s revenue recognition policy.

To date, both the Company and Betta have achieved a development milestone both valued at $2.0 million. The amounts were recognized as milestone revenue of $2.0 million and research and development cost of $2.0 million in the Company’s statement of operations for the year ended December 31, 2020. No milestones were achieved during the years ended December 31, 2023, 2022, and 2021, respectively.

Contract Assets, Liabilities, Revenues and Expenses

The following tables provide amounts by year indicated and by line item included in the Company's accompanying consolidated financial statements attributable to transactions arising from its collaboration arrangements. The dollar amounts in the tables below are in thousands.


	Third Party
	Incyte			Lilly			Other			Total
Contract assets
Accounts receivable
Balance at January 1, 2023	$	—		$	—		$	1,068		$	1,068
Billings		12,374			4,336			69		$	16,779
Cash receipts		(12,395	)		(4,336	)		(1,142	)	$	(17,873	)
Adjustments		—			—			—		$	—
Foreign exchange		21			—			5		$	26
Balance at December 31, 2023	$	-		$	-		$	-		$	-

Unbilled receivables
Balance at January 1, 2023	$	1,986		$	808		$	189		$	2,983
Accrued receivables		11,778			4,374			—		$	16,152
Billings		(12,374	)		(4,336	)		—		$	(16,710	)
Adjustments		7			(7	)		—		$	—
Foreign exchange		—			—			4		$	4
Balance at December 31, 2023	$	1,397		$	839		$	193		$	2,429

Contract liabilities
Deferred revenue
Balance at January 1, 2023	$	52,059		$	16,130		$	—		$	68,189
Addition to Deferred revenue		—			—			—		$	—
Revenue recognized in the period		(17,230	)		(10,528	)		—		$	(27,758	)
Foreign exchange		1,496			332			—		$	1,828
Balance at December 31, 2023	$	36,325		$	5,934		$	-		$	42,259
Less: current portion		(17,610	)		(5,075	)		—			(22,685	)
Non-current balance at December 31, 2023	$	18,715		$	859		$	-		$	19,574

The balance of unbilled receivables predominantly represents reimbursement revenue under the Company’s collaboration arrangements earned in the period to be billed and collected in the next period, generally quarterly.


	For the Year Ended December 31, 2023
	Third Party
	Incyte		Lilly		Other		Total
Upfront payments amortization	$	17,230	$	10,528	$	—	$	27,758
Reimbursement revenue		5,814		4,339		—	$	10,153
Milestones		5,980		—		—	$	5,980
Other		—		—		56	$	56
Total collaboration revenue		29,024		14,867		56		43,947

Operating expenses:
Research and development expense	$	24	$	—	$	—	$	24
General and administrative expense		—		—		—	$	—
Total operating expenses from collaborations		24		—		—		24

Revenue recognized that was included in deferred revenue at the beginning of the period	$	17,230	$	10,528	$	—	$	27,758

	For the Year Ended December 31, 2022
	Third Party
	Incyte		Lilly		Other		Total
Upfront payments amortization	$	16,776	$	10,281	$	222	$	27,279
Reimbursement revenue		8,602		3,634		—	$	12,236
Milestones		1,000		—		1,021	$	2,021
Other		—		—		50	$	50
Total collaboration revenue		26,378		13,915		1,293		41,586

Operating expenses:
Research and development expense	$	752	$	—	$	—	$	752
General and administrative expense		—		—		—	$	—
Total operating expenses from collaborations		752		—		—		752

Revenue recognized that was included in deferred revenue at the beginning of the period	$	16,776	$	10,048	$	222	$	27,046

	For the Year Ended December 31, 2021
	Related Party		Third Party
	Incyte		Lilly		Other		Total
Upfront payments amortization	$	18,864	$	14,012	$	602	$	14,614
Reimbursement revenue		8,740		3,332		1,057		4,389
Milestones		2,000		—		500	$	500
Total collaboration revenue	$	29,604	$	17,344	$	2,159	$	19,503

Operating expenses:
Research and development expense	$	1,223	$	—	$	151	$	151
General and administrative expense		—		—		—		—
Total operating expenses from collaborations	$	1,223	$	—	$	151	$	151

Revenue recognized that was included in deferred revenue at the beginning of the period	$	18,864	$	—	$	602	$	602

Loss per Share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Loss per Share

14. Loss per Share

The two-class method was not applied for the years ended December 31, 2023, 2022 and 2021 due to the net loss recognized in each of those periods.

Basic and diluted loss per share allocable to common stockholders are computed as follows:


	Year Ended December 31,
	2023			2022			2021
	(In thousands except per share data)
Net loss	$	(154,939	)	$	(131,194	)	$	(66,816	)
Weighted average shares outstanding		51,605,444			44,919,084			38,638,434
Basic and diluted loss per share allocable to common stockholders	$	(3.00	)	$	(2.92	)	$	(1.73	)

Loss per Share - Summary of Basic and Diluted Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net loss	$ (154,939)	$ (131,194)	$ (66,816)
Weighted average shares outstanding, basic	51,605,444	44,919,084	38,638,434
Weighted average shares outstanding, diluted	51,605,444	44,919,084	38,638,434
Basic loss per share allocable to common stockholders	$ (3)	$ (2.92)	$ (1.73)
Diluted loss per share allocable to common stockholders	$ (3)	$ (2.92)	$ (1.73)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Investments in Debt Securities - Summary of Fair Value of Debt Securities by Major Security Type (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule Of Held To Maturity Securities [Line Items]
Total	$ 231,715	$ 197,341
Unrealized Gains	467	19
Unrealized Losses	(237)	(1,015)
Fair Value	231,945	196,345
Money market funds [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	24,273	18,404
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	24,273	18,404
Corporate paper and notes [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	146,415	126,102
Unrealized Gains	425	15
Unrealized Losses	(148)	(736)
Fair Value	146,692	125,381
U.S. government agency securities [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	39,456	34,364
Unrealized Gains	24	4
Unrealized Losses	(70)	(181)
Fair Value	39,410	34,187
U.S. treasuries [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	21,571	18,471
Unrealized Gains	18	0
Unrealized Losses	(19)	(98)
Fair Value	$ 21,570	$ 18,373

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5B

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5B

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-5

+ Details

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Preparation

Principles of Consolidation

Functional and Presentation Currency

Use of Estimates

Concentration of Credit Risk

Subsequent Events

Fair Value Measurements

•

Level 1 – Quoted market prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date.

•

The asset’s or liability’s fair value measurement within the fair value hierarchy is based upon the lowest level of any input that is significant to the fair value measurement.

Going Concern

Cash and Cash Equivalents

Restricted Cash

Marketable Securities

Accounts Receivable

Accounts receivable are amounts due from collaboration partners as a result of research and development services provided or milestones achieved but not yet paid.

Allowance for Credit Losses

Property and Equipment

The Company records property and equipment at cost. The Company calculates depreciation and amortization using the straight-line method over the following estimated useful lives:


Asset Category		Useful Lives
Laboratory equipment		5 years
Office furniture and equipment		5 years
Leasehold improvements		Shorter of term of lease or 10 years

Intangible Assets

Impairment of Long-Lived Assets

Leases

Income Taxes

Deferred Taxes

Unrecognized Tax Benefits

Revenue Recognition

identify the contract(s) with a customer;

ii.

identify the performance obligations in the contract;

iii.

determine the transaction price;

iv.

allocate the transaction price to the performance obligations in the contract; and

recognize revenue when (or as) the entity satisfies a performance obligation.

performed on behalf of the collaboration partner related to the licensed targets. The Company also derives revenue from government grants.

As part of the accounting for these arrangements, the Company must use judgment to determine:

the number of performance obligations based on the determination under step (ii) above and whether those performance obligations are distinct from other performance obligations in the contract;

the transaction price under step (iii) above;

the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above;

whether the combined performance obligation is satisfied over time or at a point in time in step (v) above; and

the appropriate method for measuring progress toward complete satisfaction of a performance obligation in step (v) above.

Exclusive Licenses

Research and Development Services

Government Grants

Research and Development Expenses

Share-Based Compensation

Earnings (Loss) per Share

Segment Information

The Company operates in one reportable segment, which comprises the discovery and development of innovative therapeutics.

Recently Adopted Accounting Pronouncements

and applied the amendments of this ASU to its disclosures. The application of this ASU did not have a material impact on the Company's financial position, results of operations or cash flows.

Income Taxes - Summary of Components of Loss from Operations Before Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
United States	$ (6,117)	$ (10,437)	$ (8,502)
Netherlands	(145,630)	(119,798)	(58,075)
Loss before income tax expense	$ (151,747)	$ (130,235)	$ (66,577)

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(11))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479557/942-235-S99-1

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-SubTopic 20
-Topic 940
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481913/940-20-25-1

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

Collaborations (Tables)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Summary of Company's Accompanying Consolidated Financial Statements Attributable to Transactions Arising From Collaboration Arrangements


	Third Party
	Incyte			Lilly			Other			Total
Contract assets
Accounts receivable
Balance at January 1, 2023	$	—		$	—		$	1,068		$	1,068
Billings		12,374			4,336			69		$	16,779
Cash receipts		(12,395	)		(4,336	)		(1,142	)	$	(17,873	)
Adjustments		—			—			—		$	—
Foreign exchange		21			—			5		$	26
Balance at December 31, 2023	$	-		$	-		$	-		$	-

Unbilled receivables
Balance at January 1, 2023	$	1,986		$	808		$	189		$	2,983
Accrued receivables		11,778			4,374			—		$	16,152
Billings		(12,374	)		(4,336	)		—		$	(16,710	)
Adjustments		7			(7	)		—		$	—
Foreign exchange		—			—			4		$	4
Balance at December 31, 2023	$	1,397		$	839		$	193		$	2,429

Contract liabilities
Deferred revenue
Balance at January 1, 2023	$	52,059		$	16,130		$	—		$	68,189
Addition to Deferred revenue		—			—			—		$	—
Revenue recognized in the period		(17,230	)		(10,528	)		—		$	(27,758	)
Foreign exchange		1,496			332			—		$	1,828
Balance at December 31, 2023	$	36,325		$	5,934		$	-		$	42,259
Less: current portion		(17,610	)		(5,075	)		—			(22,685	)
Non-current balance at December 31, 2023	$	18,715		$	859		$	-		$	19,574

Summary of Company's Collaboration Arrangements Earned in Period to Be Billed and Collected in Next Period


	For the Year Ended December 31, 2023
	Third Party
	Incyte		Lilly		Other		Total
Upfront payments amortization	$	17,230	$	10,528	$	—	$	27,758
Reimbursement revenue		5,814		4,339		—	$	10,153
Milestones		5,980		—		—	$	5,980
Other		—		—		56	$	56
Total collaboration revenue		29,024		14,867		56		43,947

Operating expenses:
Research and development expense	$	24	$	—	$	—	$	24
General and administrative expense		—		—		—	$	—
Total operating expenses from collaborations		24		—		—		24

Revenue recognized that was included in deferred revenue at the beginning of the period	$	17,230	$	10,528	$	—	$	27,758

	For the Year Ended December 31, 2022
	Third Party
	Incyte		Lilly		Other		Total
Upfront payments amortization	$	16,776	$	10,281	$	222	$	27,279
Reimbursement revenue		8,602		3,634		—	$	12,236
Milestones		1,000		—		1,021	$	2,021
Other		—		—		50	$	50
Total collaboration revenue		26,378		13,915		1,293		41,586

Operating expenses:
Research and development expense	$	752	$	—	$	—	$	752
General and administrative expense		—		—		—	$	—
Total operating expenses from collaborations		752		—		—		752

Revenue recognized that was included in deferred revenue at the beginning of the period	$	16,776	$	10,048	$	222	$	27,046

	For the Year Ended December 31, 2021
	Related Party		Third Party
	Incyte		Lilly		Other		Total
Upfront payments amortization	$	18,864	$	14,012	$	602	$	14,614
Reimbursement revenue		8,740		3,332		1,057		4,389
Milestones		2,000		—		500	$	500
Total collaboration revenue	$	29,604	$	17,344	$	2,159	$	19,503

Operating expenses:
Research and development expense	$	1,223	$	—	$	151	$	151
General and administrative expense		—		—		—		—
Total operating expenses from collaborations	$	1,223	$	—	$	151	$	151

Revenue recognized that was included in deferred revenue at the beginning of the period	$	18,864	$	—	$	602	$	602

Operating Leases - Schedule of Weighted Average Remaining Lease Terms and Discount Rates (Details)	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted-average remaining operating lease term (in years)	7 years 7 months 6 days	8 years 3 months 18 days
Weighted-average discount rate for operating leases	4.80%	4.80%

Stockholders' Equity

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Stockholders' Equity

11. Stockholders’ Equity

Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to dividends when and if declared by the board of directors.

Share Issuances

On January 18, 2021, the Company sold 706,834 common shares, at a price of $28.295 for aggregate proceeds of $16.5 million.

On January 21, 2021, the Company sold 5,575,757 common shares, at a price of $24.75 for aggregate proceeds of $129.4 million.

On November 9, 2021, the Company sold 4,438,597 common shares, at a price of $28.50 for aggregate proceeds of $118.7 million.

In May 2021, the Company entered into an Open Market Sale Agreement (the “Sales Agreement”) with Jefferies LLC (“Jefferies”) to sell from time to time up to $125.0 million of the Company’s common stock through an “at the market” offering program under which Jefferies acts as the sales agent. Subject to the terms and conditions of the Sales Agreement, Jefferies could sell the common stock by any method deemed to be an “at-the-market” offering as defined in Rule 415 promulgated under the Securities Act of 1933, as amended (the “Securities Act”).

Jefferies was entitled to compensation at a commission rate of up to 3.0% of the gross proceeds of shares sold under the Sales Agreement. In connection with the sale of the common shares on our behalf, Jefferies was deemed to be an “underwriter” within the meaning of the Securities Act and the compensation of Jefferies was deemed to be underwriting commissions or discounts. The Company agreed to provide indemnification and contribution to Jefferies with respect to certain liabilities, including liabilities under the Securities Act or the Securities Exchange Act of 1934, as amended, or the Exchange Act.

As of December 31, 2022, the Company, pursuant to the Sales Agreement, had issued and sold an aggregate of 2,720,846 shares of its common stock resulting in gross proceeds of $59.5 million, before deducting sales agent fees of $1.7 million.

During the year ended December 31, 2023, the Company sold 3,272,280 shares of its common stock under the Sales Agreement for gross proceeds of approximately $65.5 million and net proceeds of approximately $63.8 million, after deducting sales agent fees. Having sold approximately $124.9 million of the $125.0 million available under the Sales Agreement, on May 22, 2023, the Company delivered written notice to Jefferies, effective as of such date, to terminate the Sales Agreement. The Company was not subject to any termination penalties related to the termination of the Sales Agreement.

On August 9, 2023, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Jefferies LLC, BofA Securities, Inc., Guggenheim Securities, LLC and William Blair & Company, L.L.C., as representatives of the several underwriters named therein (collectively, the “Underwriters”), in connection with the issuance and sale by the Company in a public offering of 6,818,182 common shares of the Company, nominal value €0.09 per share, at a public offering price of $22.00 per share, less underwriting discounts and commissions, pursuant to an effective shelf registration statement on Form S-3 and accompanying prospectus (Registration No. 333-255903), which became effective upon filing on May 7, 2021, and a prospectus supplement thereunder. Under the terms of the Underwriting Agreement, the Company also granted the Underwriters an option exercisable for 30 days to purchase up to an additional 1,022,727 common shares at the public offering price, less underwriting discounts and commissions. On August 10, 2023, the Underwriters exercised this option in full. The offering closed on August 14, 2023, and the Company received net proceeds of $162.2 million, after deducting underwriting discounts and fees.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Operating Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Summary of Components of Lease Cost

The components of lease cost recorded in the Company’s consolidated statement of operations and statement of cash flows were as follows:


	For the Year Ended December 31,
	2023		2022
	(In thousands)
Operating lease cost	$	2,256	$	2,524
Variable lease cost		190		366
Total lease cost included in operating expenses	$	2,446	$	2,890

Cash paid to lessors included in operating cash outflows	$	2,367	$	2,622

Schedule of Maturities of Operating Lease Obligations

Maturities of the Company’s operating lease obligations as of December 31, 2023 were as follows (in thousands):


Year	Operating Leases
2024	$	2,208
2025	$	2,224
2026	$	1,785
2027	$	1,563
2028	$	1,563
Thereafter	$	5,100
Total lease payments	$	14,443
Less: amount representing interest	$	(2,281	)
Total lease obligations	$	12,162

Schedule of Weighted Average Remaining Lease Terms and Discount Rates

The weighted-average remaining lease terms and discount rates related to the Company’s leases were as follows:


	As of December 31,
	2023			2022
Weighted-average remaining operating lease term (in years)		7.6			8.3
Weighted-average discount rate for operating leases		4.8	%		4.8	%