Merus (MRUS) 10-Q 5 Aug 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Jul. 30, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Entity Registrant Name	Merus N.V.
Trading Symbol	MRUS
Entity Central Index Key	0001651311
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding		38,477,796
Entity File Number	001-37773
Entity Incorporation, State or Country Code	P7
Entity Tax Identification Number	00-0000000
Entity Address, Address Line One	Yalelaan 62
Entity Address, City or Town	Utrecht
Entity Address, Postal Zip Code	3584 CM
Entity Address, Country	NL
City Area Code	+31 85
Local Phone Number	016 2500
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common shares, nominal value €0.09 per share
Security Exchange Name	NASDAQ

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 311,472	$ 163,082
Marketable securities	41,280	44,673
Accounts receivable	1,471	46
Accounts receivable (related party)	2,212	1,623
Prepaid expenses and other current assets	10,559	8,569
Total current assets	366,994	217,993
Property and equipment, net	3,596	4,115
Operating lease right-of-use assets	4,762	3,907
Intangible assets, net	2,608	2,843
Deferred tax assets	140	410
Other assets	1,483	1,949
Total assets	379,583	231,217
Current liabilities:
Accounts payable	6,160	3,126
Accrued expenses and other liabilities	24,529	21,803
Income taxes payable		206
Current portion of lease obligation	1,597	1,432
Current portion of deferred revenue	13,184	625
Current portion of deferred revenue (related party)	18,937	19,554
Total current liabilities	64,407	46,746
Lease obligation	3,198	2,521
Deferred revenue, net of current portion	25,338	237
Deferred revenue, net of current portion (related party)	67,553	79,450
Total liabilities	160,496	128,954
Commitments and contingencies - Note 6
Stockholders’ equity:
Common shares	3,959	3,211
Additional paid-in capital	649,627	490,093
Accumulated other comprehensive income	3,155	9,071
Accumulated deficit	(437,654)	(400,112)
Total stockholders’ equity	219,087	102,263
Total liabilities and stockholders’ equity	$ 379,583	$ 231,217

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - € / shares	Jun. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Common shares, par value	€ 0.09	€ 0.09
Common shares, authorized	45,000,000	45,000,000
Common shares, issued	38,444,580	31,602,953
Common shares, outstanding	38,444,580	31,602,953

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Total revenue	$ 12,379	$ 6,056	$ 20,729	$ 12,357
Operating expenses:
Research and development	24,612	13,709	45,418	30,696
General and administrative	10,569	8,043	19,902	16,925
Total operating expenses	35,181	21,752	65,320	47,621
Operating loss	(22,802)	(15,696)	(44,591)	(35,264)
Other (loss) income, net:
Interest (expense) income, net	(51)	99	(133)	379
Foreign exchange (losses) gains, net	(4,525)	(2,346)	7,678	539
Other (losses) gains, net	52		(385)
Total other (loss) income, net	(4,524)	(2,247)	7,160	918
Net loss before income taxes	(27,326)	(17,943)	(37,431)	(34,346)
Income tax expense	62	31	111	128
Net loss	(27,388)	(17,974)	(37,542)	(34,474)
Other comprehensive income (loss):
Currency translation adjustment	3,475	2,201	(5,916)	(906)
Comprehensive loss	$ (23,913)	$ (15,773)	$ (43,458)	$ (35,380)
Net loss per share attributable to common stockholders:
Basic and diluted	$ (0.71)	$ (0.54)	$ (1.01)	$ (1.22)
Weighted-average common shares outstanding:
Basic and diluted	38,376	29,034	37,299	28,990
Collaboration Revenue [Member]
Total revenue from contracts with customers	$ 5,118	$ 184	$ 6,717	$ 512
Collaboration Revenue (Related Party) [Member]
Total revenue from contracts with customers	$ 7,261	$ 5,872	$ 14,012	$ 11,845

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (37,542)	$ (34,474)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization of property and equipment	634	532
Amortization of intangible assets	147	134
Foreign exchange gain	(7,611)	(503)
Loss on disposal of property and equipment	0	16
Stock-based compensation expense	7,959	3,483
Amortization of premium (discount) on investments	48	(79)
Deferred tax expense	270	78
Changes in operating assets and liabilities:
Accounts receivable	(2,097)	681
Operating lease right-of-use assets and lease obligations	(11)	3
Prepaid expenses and other current assets	(1,852)	(6,441)
Accounts payable	3,190	(599)
Accrued expenses and other liabilities	3,207	2,556
Deferred revenue	28,704	(9,255)
Net cash used in operating activities	(4,954)	(43,868)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of marketable securities	(24,850)	(28,947)
Proceeds from maturities of marketable securities	28,163	28,181
Purchases of property and equipment	(260)	(512)
Net cash provided by (used in) investing activities	3,053	(1,278)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payment of offering costs	0	(164)
Proceeds from issuance of common stock, net	129,398	0
Proceeds from stock options exercised	6,728	893
Repurchase of restricted stock units	(285)	0
Net cash provided by financing activities	152,318	729
Foreign exchange impact on cash, cash equivalents and restricted cash	(2,027)	(1,107)
Net increase (decrease) in cash, cash equivalents and restricted cash	148,390	(45,524)
Cash, cash equivalents, and restricted cash, beginning of period	163,283	197,813
Cash, cash equivalents, and restricted cash, end of period	311,673	152,289
SUPPLEMENTAL DISCLOSURES:
Non-cash right-of-use assets acquired from operating lease obligations	1,662	0
Income taxes paid	491	25
Non-cash purchases of property, equipment and intangibles	22	35
Non-cash issuance of stock options	573	0
CASH, CASH EQUIVALENTS AND RESTRICTED CASH
Cash and cash equivalents	311,472	152,088
Restricted cash included in non-current other assets	201	201
Cash, cash equivalents, and restricted cash, end of period	311,673	152,289
Lilly
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net	$ 16,477	$ 0

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Lilly	Common Stock [Member]	Common Stock [Member]Lilly	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]Lilly	Accumulated Deficit [Member]	Accumulated Deficit [Member]Lilly	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]Lilly
Beginning balance at Dec. 31, 2019	$ 131,300		$ 2,918		$ 441,395		$ (314,599)		$ 1,586
Beginning balance, shares at Dec. 31, 2019			28,882,217
Exercise of stock options and vesting of restricted stock units	602		$ 13		589
Exercise of stock options and vesting of restricted stock units, shares			127,205
Stock-based compensation	2,291				2,291
Currency translation adjustment	(3,107)								(3,107)
Net loss	(16,500)						(16,500)
Ending balance at Mar. 31, 2020	114,586		$ 2,931		444,275		(331,099)		(1,521)
Ending balance, shares at Mar. 31, 2020			29,009,422
Beginning balance at Dec. 31, 2019	131,300		$ 2,918		441,395		(314,599)		1,586
Beginning balance, shares at Dec. 31, 2019			28,882,217
Currency translation adjustment	(906)
Net loss	(34,474)
Ending balance at Jun. 30, 2020	100,296		$ 2,935		445,754		(349,073)		680
Ending balance, shares at Jun. 30, 2020			29,047,344
Beginning balance at Mar. 31, 2020	114,586		$ 2,931		444,275		(331,099)		(1,521)
Beginning balance, shares at Mar. 31, 2020			29,009,422
Exercise of stock options and vesting of restricted stock units	291		$ 4		287		0		0
Exercise of stock options and vesting of restricted stock units, shares			37,922
Stock-based compensation	1,192		$ 0		1,192		0		0
Currency translation adjustment	2,201		0		0		0		2,201
Net loss	(17,974)		0		0		(17,974)		0
Ending balance at Jun. 30, 2020	100,296		$ 2,935		445,754		(349,073)		680
Ending balance, shares at Jun. 30, 2020			29,047,344
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	129,403	$ 16,477	$ 610	$ 77	128,793	$ 16,400		$ 0		$ 0
Issuance of common stock, shares			5,575,757	706,834
Exercise of stock options and vesting of restricted stock units	4,824		$ 42		4,782
Exercise of stock options and vesting of restricted stock units, shares			386,097
Repurchase of restricted stock units	(285)				(285)
Stock-based compensation	3,400				3,400
Currency translation adjustment	(9,391)								(9,391)
Net loss	(10,154)						(10,154)
Ending balance at Mar. 31, 2021	236,537		$ 3,940		643,183		(410,266)		(320)
Ending balance, shares at Mar. 31, 2021			38,271,641
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
Currency translation adjustment	(5,916)
Net loss	(37,542)
Ending balance at Jun. 30, 2021	219,087		$ 3,959		649,627		(437,654)		3,155
Ending balance, shares at Jun. 30, 2021			38,444,580
Beginning balance at Mar. 31, 2021	236,537		$ 3,940		643,183		(410,266)		(320)
Beginning balance, shares at Mar. 31, 2021			38,271,641
Exercise of stock options and vesting of restricted stock units	1,904		$ 19		1,885		0		0
Exercise of stock options and vesting of restricted stock units, shares			172,939
Stock-based compensation	4,559		$ 0		4,559		0		0
Currency translation adjustment	3,475		0		0		0		3,475
Net loss	(27,388)		0		0		(27,388)		0
Ending balance at Jun. 30, 2021	$ 219,087		$ 3,959		$ 649,627		$ (437,654)		$ 3,155
Ending balance, shares at Jun. 30, 2021			38,444,580

Overview

Overview	6 Months Ended
	Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Overview	1. Overview 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 $437.7 million as of June 30, 2021. 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. On January 21, 2021, the Company completed an offering of common shares in which the Company sold 5,575,757 common shares, including 727,272 common shares pursuant to the underwriters’ option to purchase additional shares, at a price to the public of $24.75 for aggregate net proceeds of $129.4 million. Based on the Company’s current operating plan, the Company expects that its existing cash and cash equivalents and marketable securities of $352.8 million as of June 30, 2021, will fund the Company’s operations into the second half of 2024.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The principal accounting policies applied in the preparation of these unaudited condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2020, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 16, 2021 (the “Annual Report on Form 10-K”). There have been no material changes in the Company’s significant accounting policies during the six months ended June 30, 2021. Basis of Presentation The Company prepared its unaudited consolidated condensed 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"). The unaudited condensed consolidated financial statements include the accounts of Merus N.V. and its wholly owned, controlled subsidiary, Merus US, Inc. All intercompany transactions and balances of subsidiaries have been eliminated in consolidation. In the opinion of management, these financial statements reflect all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the unaudited condensed consolidated financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The three months ended June 30, 2021 and 2020 are referred to as the second quarter of 2021 and 2020, respectively. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. The unaudited condensed consolidated financial statements presented herein do not contain the required disclosures under U.S. GAAP for annual financial statements. Therefore, these unaudited condensed consolidated financial statements should be read in conjunction with the annual audited consolidated financial statements and related notes as of and for the year ended December 31, 2020, included in the Annual Report on Form 10-K. 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 securities balances. After considering the Company’s current research and development plans, 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 June 30, 2021, 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. Recently Adopted Accounting Pronouncements In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808)

Investments in Debt Securities

Investments in Debt Securities	6 Months Ended
	Jun. 30, 2021
Debt Securities [Abstract]
Investments in Debt Securities	3. Investments in Debt Securities The following tables summarize the Company’s investments in debt securities and their presentation in the condensed consolidated balance sheet: June 30, 2021 December 31, 2020 (in thousands) Money market funds $ 14,106 $ 10,156 Corporate paper and notes 43,746 27,978 U.S. government agency securities — 9,150 U.S. treasuries 2,534 15,043 Total $ 60,386 $ 62,327 Fair value of debt securities $ 60,386 $ 62,328 June 30, 2021 December 31, 2020 (in thousands) Cash equivalents $ 19,106 $ 17,654 Current marketable securities 41,280 44,673 Total $ 60,386 $ 62,327 The Company does not intend to sell and believes it is unlikely that the Company will be required to sell the above investments before recovery of their amortized cost bases, which may be at maturity. The Company determined that there was no material change in the credit risk of any of its investments. 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).

Supplemental Balance Sheet Info

Supplemental Balance Sheet Information	6 Months Ended
	Jun. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Supplemental Balance Sheet Information	4. Supplemental Balance Sheet Information Prepaid expenses and other current assets consisted of the following: June 30, 2021 December 31, 2020 (In thousands) Prepaid clinical and manufacturing costs $ 3,261 $ 4,971 Prepaid general and administrative expenses 5,923 2,460 Interest receivable 7 80 Other 1,368 1,058 Total $ 10,559 $ 8,569 Accrued expenses and other liabilities consisted of the following: June 30, 2021 December 31, 2020 (In thousands) Accrued research and development expenses $ 19,570 $ 15,372 Accrued general and administrative expenses 1,885 1,566 Accrued personnel costs 2,681 4,854 Other 393 11 Total $ 24,529 $ 21,803

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	5. Income Taxes The Company files income tax returns in the U.S. federal and Massachusetts jurisdictions as well as in the Netherlands. The components of the income tax expense (benefit) from continuing operations are as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 (In thousands) (In thousands) U.S. federal $ 114 $ 94 $ (112 ) $ 38 U.S. state 47 36 (47 ) 12 Total current income tax (benefit) expense $ 161 $ 130 $ (159 ) $ 50 U.S. federal $ (54 ) $ (63 ) $ 207 $ 62 U.S. state (45 ) (36 ) 63 16 Total deferred income tax (benefit) expense $ (99 ) $ (99 ) $ 270 $ 78 Total income tax expense $ 62 $ 31 $ 111 $ 128 After consideration of all positive and negative evidence, we believe that it is more-likely-than-not that the Netherlands deferred tax assets, that are not supported by reversing temporary differences, will not be realized. As a result, we established a full valuation allowance against deferred tax assets of the Netherlands.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Litigation On April 5, 2018, an unnamed third party filed a notice of opposition against the Company’s EP 2604625 patent, entitled “Generation of Binding Molecules,” in the European Opposition Division of the European Patent Office (the “EPO”). The notice asserted, as applicable, added subject matter, lack of novelty, lack of inventive step, and insufficiency. On August 20, 2018, the Company timely responded to these submissions. An opposition hearing was held in June 2019, wherein the EPO revoked the EP 2604625 patent in its entirety under Art. 123(2) EPC. The Company timely appealed that decision in December 2019 before the Technical Board of Appeals for the EPO seeking reinstatement of the patent and proposing auxiliary requests for certain amended claims, with further proceedings to be scheduled in the future. As this opposition proceeding continues, the Company cannot be certain that it will ultimately prevail. From time to time, the Company may be involved in various other claims and legal proceedings relating to claims arising out of the Company’s operations. The Company is not currently a party to any material legal proceedings.

Leases

Leases	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Leases	7. Leases The Company has noncancelable operating leases for offices and lab spaces expiring at various dates through 2026. The components of lease expense for the three and six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 (In thousands) (In thousands) Lease cost Operating lease cost $ 434 $ 396 $ 852 $ 792 Variable lease cost 132 107 223 189 Total lease cost included in operating expenses $ 566 $ 503 $ 1,075 $ 981 Other information Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows $ 428 $ 396 $ 863 $ 789 During the six months ended June 30, 2021, the Company signed a lease amendment (the “Amendment”) for offices and lab spaces in Utrecht, Netherlands. The Amendment extended the lease term by approximately 1.5 years ending at the end of March 2023 and did not include additional right-of-use other than the extended lease term.

Collaborations

Collaborations	6 Months Ended
	Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborations	8. 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. At inception of the arrangement, Lilly had selected its first target. The objective of each program would be 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 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 Eli 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 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 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 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 i n 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. As of June 30, 2021, no milestones have been achieved. Incyte On January 23, 2017, the Company completed the sale of shares and exchange of a license with Incyte Corporation (“Incyte”). 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 ® At June 30, 2021, the Company is currently engaged in clinical development activities for MCLA-145 and developing pre-clinical candidates for the other programs. No development or commercialization milestones have been achieved to date. ONO On March 14, 2018, the Company granted ONO Pharmaceuticals 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 ® Amounts related to the provision of a license are amortized over the intended period of use. 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 ® 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. To date, the Company has achieved two milestones under this agreement and has received an aggregate of $1.3 million in milestone payments. Research and development activities are on-going as of June 30, 2021. Contract Assets and Liabilities The following tables provide amounts by year indicated and by line item included in the Company's accompanying condensed consolidated financial statements attributable to transactions arising from its collaboration arrangements. The dollar amounts in the tables below are in thousands. Related Party Third Party Incyte Lilly Other Total CONTRACT ASSETS Accounts receivable Balance at January 1, 2021 $ — $ — $ 46 $ 46 Billings 3,195 60,254 — 60,254 Cash receipts (3,195 ) (60,000 ) — (60,000 ) Adjustments — — — — Foreign exchange — (1 ) (4 ) (5 ) Balance at June 30, 2021 — 253 42 295 Unbilled receivables Balance at January 1, 2021 $ 1,623 $ — $ — $ — Accrued receivables 3,848 1,129 323 1,452 Billings (3,194 ) (254 ) — (254 ) Adjustments — — — — Foreign exchange (65 ) (17 ) (5 ) (22 ) Balance at June 30, 2021 2,212 858 318 1,176 CONTRACT LIABILITIES Deferred revenue Balance at January 1, 2021 $ 99,004 $ — $ 862 $ 862 Allocation of contract consideration — 43,523 — 43,523 Revenue recognized in the period (9,525 ) (4,911 ) (352 ) (5,263 ) Foreign exchange (2,989 ) (578 ) (22 ) (600 ) Balance at June 30, 2021 86,490 38,034 488 38,522 Less: current portion (18,937 ) (12,716 ) (468 ) (13,184 ) Non-current balance at June 30, 2021 67,553 25,318 20 25,338 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. Incyte is a related party as more fully described in Note 10. Contract Revenues and Expenses Three Months Ended June 30, 2021 (In thousands) Related Party Third Party Incyte Lilly Other Total Upfront payments $ 4,791 $ 3,765 $ 162 $ 3,927 Reimbursement revenue 2,470 869 322 1,191 Milestones — — — — Total collaboration revenue $ 7,261 $ 4,634 $ 484 $ 5,118 Operating expenses: Research and development expense $ 289 $ — $ — $ — General and administrative expense — — — — Total operating expenses from collaborations $ 289 $ — $ — $ — Revenue recognized that was included in deferred revenue at the beginning of the period $ 4,791 $ 3,765 $ 162 $ 3,927 Three Months Ended June 30, 2020 (In thousands) Related Party Third Party Incyte Lilly Other Total Upfront payments $ 4,363 $ — $ 284 $ 284 Reimbursement revenue 1,509 — (105 ) (105 ) Milestones — — 5 5 Total collaboration revenue $ 5,872 $ — $ 184 $ 184 Operating expenses: Research and development expense $ 612 $ — $ — $ — General and administrative expense — — — — Total operating expenses from collaborations $ 612 $ — $ — $ — Revenue recognized that was included in deferred revenue at the beginning of the period $ 4,363 $ — $ 289 $ 289 Six Months Ended June 30, 2021 (In thousands) Related Party Third Party Incyte Lilly Other Total Upfront payments $ 9,525 $ 4,911 $ 352 $ 5,263 Reimbursement revenue 4,487 1,132 322 1,454 Milestones — — — — Total collaboration revenue $ 14,012 $ 6,043 $ 674 $ 6,717 Operating expenses: Research and development expense $ 648 $ — $ — $ — General and administrative expense — — — — Total operating expenses from collaborations $ 648 $ — $ — $ — Revenue recognized that was included in deferred revenue at the beginning of the period $ 9,525 $ — $ 352 $ 352 Six Months Ended June 30, 2020 (In thousands) Related Party Third Party Incyte Lilly Other Total Upfront payments $ 8,731 $ — $ 483 $ 483 Reimbursement revenue 3,114 — (11 ) (11 ) Milestones — — 40 40 Total collaboration revenue $ 11,845 $ — $ 512 $ 512 Operating expenses: Research and development expense $ 764 $ — $ — $ — General and administrative expense — — — — Total operating expenses from collaborations $ 764 $ — $ — $ — Revenue recognized that was included in deferred revenue at the beginning of the period $ 8,731 $ — $ 523 $ 523

Employee Benefits

Employee Benefits	6 Months Ended
	Jun. 30, 2021
Compensation And Retirement Disclosure [Abstract]
Employee Benefits	9. Employee Benefits Stock-Based Compensation Stock-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 (In thousands) (In thousands) Research and development $ 1,850 $ (261 ) $ 3,487 $ 762 General and administrative 2,709 1,453 4,472 2,721 Total $ 4,559 $ 1,192 $ 7,959 $ 3,483 The weighted-average grant date fair value of options, estimated as of the grant date using the Black Scholes option pricing model was $17.42 per option for the 1,312,810 options granted during the six months ended June 30, 2021. The following assumptions were used to estimate the fair value of the options granted during the six months ended June 30, 2021. Volatility 87.2 % Risk-free interest rate 0.6 % Expected holding period (in years) 6.1 Dividend yield - In addition, the Company granted 9,976 RSUs during the six months ended June 30, 2021 with a weighted average grant date fair value of $20.15 per unit. Executive Settlement 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 stock-based compensation expense in respect of share-based payments in research and development expense in the consolidated statement of operations in the prior year. 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. 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 $0.4 million net loss associated with the derivative instrument included as other income in the statement of operations for the six months ended June 30, 2021.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	10. Related Party Transactions The Company has entered into the Incyte collaboration and license agreement and the Incyte share subscription agreement with amounts related to transactions under the arrangement disclosed in Note 8 and the arrangement described in the Company’s annual consolidated financial statements for the year ended December 31, 2020. Incyte is a shareholder with holdings representing approximately 9.2% of the outstanding shares of the Company as of June 30, 2021, and 10.1% as of December 31, 2020.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Preparation	Basis of Presentation The Company prepared its unaudited consolidated condensed 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"). The unaudited condensed consolidated financial statements include the accounts of Merus N.V. and its wholly owned, controlled subsidiary, Merus US, Inc. All intercompany transactions and balances of subsidiaries have been eliminated in consolidation. In the opinion of management, these financial statements reflect all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the unaudited condensed consolidated financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The three months ended June 30, 2021 and 2020 are referred to as the second quarter of 2021 and 2020, respectively. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. The unaudited condensed consolidated financial statements presented herein do not contain the required disclosures under U.S. GAAP for annual financial statements. Therefore, these unaudited condensed consolidated financial statements should be read in conjunction with the annual audited consolidated financial statements and related notes as of and for the year ended December 31, 2020, included in the Annual Report on Form 10-K.
Going Concern	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 securities balances. After considering the Company’s current research and development plans, 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 June 30, 2021, 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.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808)

Investments in Debt Securities

Investments in Debt Securities (Tables)	6 Months Ended
	Jun. 30, 2021
Debt Securities [Abstract]
Summary of Investments in Debt Securities in Condensed Consolidated Balance Sheet	The following tables summarize the Company’s investments in debt securities and their presentation in the condensed consolidated balance sheet: June 30, 2021 December 31, 2020 (in thousands) Money market funds $ 14,106 $ 10,156 Corporate paper and notes 43,746 27,978 U.S. government agency securities — 9,150 U.S. treasuries 2,534 15,043 Total $ 60,386 $ 62,327 Fair value of debt securities $ 60,386 $ 62,328 June 30, 2021 December 31, 2020 (in thousands) Cash equivalents $ 19,106 $ 17,654 Current marketable securities 41,280 44,673 Total $ 60,386 $ 62,327

Supplemental Balance Sheet In_2

Supplemental Balance Sheet Information (Tables)	6 Months Ended
	Jun. 30, 2021
Balance Sheet Related Disclosures [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following: June 30, 2021 December 31, 2020 (In thousands) Prepaid clinical and manufacturing costs $ 3,261 $ 4,971 Prepaid general and administrative expenses 5,923 2,460 Interest receivable 7 80 Other 1,368 1,058 Total $ 10,559 $ 8,569
Summary of Accrued Expenses and Other Liabilities	Accrued expenses and other liabilities consisted of the following: June 30, 2021 December 31, 2020 (In thousands) Accrued research and development expenses $ 19,570 $ 15,372 Accrued general and administrative expenses 1,885 1,566 Accrued personnel costs 2,681 4,854 Other 393 11 Total $ 24,529 $ 21,803

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Summary of Components of Expense for (Benefit) from Income Taxes	The components of the income tax expense (benefit) from continuing operations are as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 (In thousands) (In thousands) U.S. federal $ 114 $ 94 $ (112 ) $ 38 U.S. state 47 36 (47 ) 12 Total current income tax (benefit) expense $ 161 $ 130 $ (159 ) $ 50 U.S. federal $ (54 ) $ (63 ) $ 207 $ 62 U.S. state (45 ) (36 ) 63 16 Total deferred income tax (benefit) expense $ (99 ) $ (99 ) $ 270 $ 78 Total income tax expense $ 62 $ 31 $ 111 $ 128

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Summary of Components of Lease Expense	The components of lease expense for the three and six months ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 (In thousands) (In thousands) Lease cost Operating lease cost $ 434 $ 396 $ 852 $ 792 Variable lease cost 132 107 223 189 Total lease cost included in operating expenses $ 566 $ 503 $ 1,075 $ 981 Other information Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows $ 428 $ 396 $ 863 $ 789

Collaborations (Tables)

Collaborations (Tables)	6 Months Ended
	Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Company's Accompanying Condensed Consolidated Financial Statements Attributable to Transactions Arising From Collaboration Arrangements	The following tables provide amounts by year indicated and by line item included in the Company's accompanying condensed consolidated financial statements attributable to transactions arising from its collaboration arrangements. The dollar amounts in the tables below are in thousands. Related Party Third Party Incyte Lilly Other Total CONTRACT ASSETS Accounts receivable Balance at January 1, 2021 $ — $ — $ 46 $ 46 Billings 3,195 60,254 — 60,254 Cash receipts (3,195 ) (60,000 ) — (60,000 ) Adjustments — — — — Foreign exchange — (1 ) (4 ) (5 ) Balance at June 30, 2021 — 253 42 295 Unbilled receivables Balance at January 1, 2021 $ 1,623 $ — $ — $ — Accrued receivables 3,848 1,129 323 1,452 Billings (3,194 ) (254 ) — (254 ) Adjustments — — — — Foreign exchange (65 ) (17 ) (5 ) (22 ) Balance at June 30, 2021 2,212 858 318 1,176 CONTRACT LIABILITIES Deferred revenue Balance at January 1, 2021 $ 99,004 $ — $ 862 $ 862 Allocation of contract consideration — 43,523 — 43,523 Revenue recognized in the period (9,525 ) (4,911 ) (352 ) (5,263 ) Foreign exchange (2,989 ) (578 ) (22 ) (600 ) Balance at June 30, 2021 86,490 38,034 488 38,522 Less: current portion (18,937 ) (12,716 ) (468 ) (13,184 ) Non-current balance at June 30, 2021 67,553 25,318 20 25,338
Summary of Company's Collaboration Arrangements Earned in Period to Be Billed and Collected in Next Period	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. Incyte is a related party as more fully described in Note 10. Contract Revenues and Expenses Three Months Ended June 30, 2021 (In thousands) Related Party Third Party Incyte Lilly Other Total Upfront payments $ 4,791 $ 3,765 $ 162 $ 3,927 Reimbursement revenue 2,470 869 322 1,191 Milestones — — — — Total collaboration revenue $ 7,261 $ 4,634 $ 484 $ 5,118 Operating expenses: Research and development expense $ 289 $ — $ — $ — General and administrative expense — — — — Total operating expenses from collaborations $ 289 $ — $ — $ — Revenue recognized that was included in deferred revenue at the beginning of the period $ 4,791 $ 3,765 $ 162 $ 3,927 Three Months Ended June 30, 2020 (In thousands) Related Party Third Party Incyte Lilly Other Total Upfront payments $ 4,363 $ — $ 284 $ 284 Reimbursement revenue 1,509 — (105 ) (105 ) Milestones — — 5 5 Total collaboration revenue $ 5,872 $ — $ 184 $ 184 Operating expenses: Research and development expense $ 612 $ — $ — $ — General and administrative expense — — — — Total operating expenses from collaborations $ 612 $ — $ — $ — Revenue recognized that was included in deferred revenue at the beginning of the period $ 4,363 $ — $ 289 $ 289 Six Months Ended June 30, 2021 (In thousands) Related Party Third Party Incyte Lilly Other Total Upfront payments $ 9,525 $ 4,911 $ 352 $ 5,263 Reimbursement revenue 4,487 1,132 322 1,454 Milestones — — — — Total collaboration revenue $ 14,012 $ 6,043 $ 674 $ 6,717 Operating expenses: Research and development expense $ 648 $ — $ — $ — General and administrative expense — — — — Total operating expenses from collaborations $ 648 $ — $ — $ — Revenue recognized that was included in deferred revenue at the beginning of the period $ 9,525 $ — $ 352 $ 352 Six Months Ended June 30, 2020 (In thousands) Related Party Third Party Incyte Lilly Other Total Upfront payments $ 8,731 $ — $ 483 $ 483 Reimbursement revenue 3,114 — (11 ) (11 ) Milestones — — 40 40 Total collaboration revenue $ 11,845 $ — $ 512 $ 512 Operating expenses: Research and development expense $ 764 $ — $ — $ — General and administrative expense — — — — Total operating expenses from collaborations $ 764 $ — $ — $ — Revenue recognized that was included in deferred revenue at the beginning of the period $ 8,731 $ — $ 523 $ 523

Employee Benefits (Tables)

Employee Benefits (Tables)	6 Months Ended
	Jun. 30, 2021
Compensation And Retirement Disclosure [Abstract]
Summary of Stock-based Compensation Expense Classified in Condensed Consolidated Statements of Operations and Comprehensive Loss	Stock-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 (In thousands) (In thousands) Research and development $ 1,850 $ (261 ) $ 3,487 $ 762 General and administrative 2,709 1,453 4,472 2,721 Total $ 4,559 $ 1,192 $ 7,959 $ 3,483
Summary of Assumptions Used to Estimate Fair Value of Options Granted	The following assumptions were used to estimate the fair value of the options granted during the six months ended June 30, 2021. Volatility 87.2 % Risk-free interest rate 0.6 % Expected holding period (in years) 6.1 Dividend yield -

Overview - Additional Informati

Overview - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 21, 2021	Jun. 30, 2021	Dec. 31, 2020
Organization Consolidation and Presentation of Financial Statements [Line Items]
Accumulated deficit		$ (437,654)	$ (400,112)
Cash and cash equivalents and marketable securities		$ 352,800
Underwritten Public Offering
Organization Consolidation and Presentation of Financial Statements [Line Items]
Issuance of common stock, shares	5,575,757
Number of common shares pursuant to underwriters' option to purchase additional shares	727,272
Issue price per share	$ 24.75
Net proceeds from public offering	$ 129,400

Investments in Debt Securitie_2

Investments in Debt Securities - Summary of Investments in Debt Securities in Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule Of Held To Maturity Securities [Line Items]
Total	$ 60,386	$ 62,327
Fair value of debt securities	60,386	62,328
Cash equivalents [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	19,106	17,654
Current marketable securities [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	41,280	44,673
Money market funds [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	14,106	10,156
Corporate paper and notes [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	43,746	27,978
U.S. government agency securities [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	0	9,150
U.S. treasuries [member]
Schedule Of Held To Maturity Securities [Line Items]
Total	$ 2,534	$ 15,043

Supplemental Balance Sheet In_3

Supplemental Balance Sheet Information - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Prepaid Expense And Other Assets Current [Abstract]
Prepaid clinical and manufacturing costs	$ 3,261	$ 4,971
Prepaid general and administrative expenses	5,923	2,460
Interest receivable	7	80
Other	1,368	1,058
Total	$ 10,559	$ 8,569

Supplemental Balance Sheet In_4

Supplemental Balance Sheet Information - Summary of Accrued Expenses and Other Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued research and development expenses	$ 19,570	$ 15,372
Accrued general and administrative expenses	1,885	1,566
Accrued personnel costs	2,681	4,854
Other	393	11
Total	$ 24,529	$ 21,803

Income Taxes - Summary of Compo

Income Taxes - Summary of Components of Expense for (Benefit) from Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Tax Disclosure [Abstract]
U.S. federal	$ 114	$ 94	$ (112)	$ 38
U.S. state	47	36	(47)	12
Total current income tax (benefit) expense	161	130	(159)	50
U.S. federal	(54)	(63)	207	62
U.S. state	(45)	(36)	63	16
Total deferred income tax (benefit) expense	(99)	(99)	270	78
Total income tax expense	$ 62	$ 31	$ 111	$ 128

Leases - Summary of Components

Leases - Summary of Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lease cost
Operating lease cost	$ 434	$ 396	$ 852	$ 792
Variable lease cost	132	107	223	189
Total lease cost included in operating expenses	566	503	1,075	981
Other information
Cash paid for amounts included in the measurement of lease liabilities included in operating cash flows	$ 428	$ 396	$ 863	$ 789

Leases - Additional Information

Leases - Additional Information (Details)	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Extended lease term	1 year 5 months
Amended lease term description	the Company signed a lease amendment (the “Amendment”) for offices and lab spaces in Utrecht, Netherlands. The Amendment extended the lease term by approximately 1.5 years ending at the end of March 2023 and did not include additional right-of-use other than the extended lease term.

Collaborations - Additional Inf

Collaborations - Additional Information (Details) $ / shares in Units, $ in Thousands, € in Millions	Jan. 18, 2021USD ($)$ / sharesshares	Aug. 31, 2018USD ($)	Mar. 14, 2018EUR (€)	Jan. 23, 2017USD ($)	Jan. 31, 2018USD ($)AntibodyPerformanceObligationMilestone	Mar. 31, 2021USD ($)	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Feb. 12, 2021USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from issuance of common stock, net							$ 129,398	$ 0
Net fair value of shares						$ 285
Lilly Collaborations Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment receivable	$ 40,000
Issuance of common stock, shares | shares	706,834
Common stock stated purchase price per share | $ / shares	$ 28.295
Proceeds from issuance of common stock, net	$ 20,000
Fixed consideration	43,500								$ 43,500
Upfront payment	40,000
Net fair value of shares	$ 16,500
Incyte Collaboration and License Agreement | License and Related Activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborations, transaction price as deferred revenue				$ 152,600
Second ONO Research and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable upfront payment receivable | €			€ 0.7
Payment to compensate research services | €			0.3
Over time payment for full time equivalent funding | €			€ 0.2
Simcere Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of bispecific antibodies under collaboration and license agreement | Antibody					3
Non-refundable upfront payment received					$ 2,750
Collaborations, transaction price as revenue					$ 2,750
Milestone payments received		$ 1,300
Number of milestones achieved | Milestone					2
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

Collaborations - Summary of Com

Collaborations - Summary of Company's Accompanying Condensed Consolidated Financial Statements Attributable to Transactions Arising From Collaboration Arrangements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in the period	$ 4,791	$ 4,363	$ 9,525	$ 8,731
Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in the period	3,765	0	0	0
Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in the period	162	289	352	523
Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in the period	3,927	$ 289	352	$ 523
Accounts Receivable | Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			0
Billings			3,195
Cash receipts			(3,195)
Adjustments			0
Foreign exchange			0
Balance at June 30, 2021	0		0
Accounts Receivable | Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			0
Billings			60,254
Cash receipts			(60,000)
Adjustments			0
Foreign exchange			(1)
Balance at June 30, 2021	253		253
Accounts Receivable | Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			46
Billings			0
Cash receipts			0
Adjustments			0
Foreign exchange			(4)
Balance at June 30, 2021	42		42
Accounts Receivable | Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			46
Billings			60,254
Cash receipts			(60,000)
Adjustments			0
Foreign exchange			(5)
Balance at June 30, 2021	295		295
Unbilled Receivables | Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			1,623
Accrued receivables			3,848
Billings			(3,194)
Adjustments			0
Foreign exchange			(65)
Balance at June 30, 2021	2,212		2,212
Unbilled Receivables | Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			0
Accrued receivables			1,129
Billings			(254)
Adjustments			0
Foreign exchange			(17)
Balance at June 30, 2021	858		858
Unbilled Receivables | Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			0
Accrued receivables			323
Billings			0
Adjustments			0
Foreign exchange			(5)
Balance at June 30, 2021	318		318
Unbilled Receivables | Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			0
Accrued receivables			1,452
Billings			(254)
Adjustments			0
Foreign exchange			(22)
Balance at June 30, 2021	1,176		1,176
Deferred Revenue | Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			99,004
Allocation of contract consideration			0
Revenue recognized in the period			(9,525)
Foreign exchange			(2,989)
Balance at June 30, 2021	86,490		86,490
Less: current portion	(18,937)		(18,937)
Non-current balance at June 30, 2021	67,553		67,553
Deferred Revenue | Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			0
Allocation of contract consideration			43,523
Revenue recognized in the period			(4,911)
Foreign exchange			(578)
Balance at June 30, 2021	38,034		38,034
Less: current portion	(12,716)		(12,716)
Non-current balance at June 30, 2021	25,318		25,318
Deferred Revenue | Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			862
Allocation of contract consideration			0
Revenue recognized in the period			(352)
Foreign exchange			(22)
Balance at June 30, 2021	488		488
Less: current portion	(468)		(468)
Non-current balance at June 30, 2021	20		20
Deferred Revenue | Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance at January 1, 2021			862
Allocation of contract consideration			43,523
Revenue recognized in the period			(5,263)
Foreign exchange			(600)
Balance at June 30, 2021	38,522		38,522
Less: current portion	(13,184)		(13,184)
Non-current balance at June 30, 2021	$ 25,338		$ 25,338

Collaborations - Summary of C_2

Collaborations - Summary of Company's Collaboration Arrangements Earned in Period to Be Billed and Collected in Next Period (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating expenses:
Research and development	$ 24,612	$ 13,709	$ 45,418	$ 30,696
General and administrative	10,569	8,043	19,902	16,925
Total operating expenses	35,181	21,752	65,320	47,621
Incyte
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments	4,791	4,363	9,525	8,731
Reimbursement revenue	2,470	1,509	4,487	3,114
Milestones	0	0	0	0
Total collaboration revenue	7,261	5,872	14,012	11,845
Operating expenses:
Research and development	289	612	648	764
General and administrative	0	0	0	0
Total operating expenses	289	612	648	764
Revenue recognized in the period	4,791	4,363	9,525	8,731
Lilly
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments	3,765	0	4,911	0
Reimbursement revenue	869	0	1,132	0
Milestones	0	0	0	0
Total collaboration revenue	4,634	0	6,043	0
Operating expenses:
Research and development	0	0	0	0
General and administrative	0	0	0	0
Total operating expenses	0	0	0	0
Revenue recognized in the period	3,765	0	0	0
Other
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments	162	284	352	483
Reimbursement revenue	322	(105)	322	(11)
Milestones	0	5	0	40
Total collaboration revenue	484	184	674	512
Operating expenses:
Research and development	0	0	0	0
General and administrative	0	0	0	0
Total operating expenses	0	0	0	0
Revenue recognized in the period	162	289	352	523
Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments	3,927	284	5,263	483
Reimbursement revenue	1,191	(105)	1,454	(11)
Milestones	0	5	0	40
Total collaboration revenue	5,118	184	6,717	512
Operating expenses:
Research and development	0	0	0	0
General and administrative	0	0	0	0
Total operating expenses	0	0	0	0
Revenue recognized in the period	$ 3,927	$ 289	$ 352	$ 523

Employee Benefits - Summary of

Employee Benefits - Summary of Stock-based Compensation Expense Classified in Condensed Consolidated Statements of Operations and Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total	$ 4,559	$ 1,192	$ 7,959	$ 3,483
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total	1,850	(261)	3,487	762
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total	$ 2,709	$ 1,453	$ 4,472	$ 2,721

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Apr. 30, 2020	Mar. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average fair value of options granted			$ 17.42
Share-based payment award, fair value assumptions, method used			Black Scholes option pricing model
Number of options granted			1,312,810
Severance payment				$ 0.1
Additional compensation cost		$ 0.2
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Net reversal of stock-based compensation expense				$ 0.4
Other Income
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Net loss associated with the derivative instrument			$ 0.4
Postemployment Retirement Benefits
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Executive settlements, cash compensation paid	$ 0.3
RSUs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation, RSUs granted			9,976
Weighted average grant date fair value			$ 20.15

Employee Benefits - Summary o_2

Employee Benefits - Summary of Assumptions Used to Estimate Fair Value of Options Granted (Details)	6 Months Ended
	Jun. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Volatility	87.20%
Risk-free interest rate	0.60%
Expected holding period (in years)	6 years 1 month 6 days

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details)	Jun. 30, 2021	Dec. 31, 2020
Incyte | Merus N V [Member]
Related Party Transaction [Line Items]
Ownership percentage	9.20%	10.10%