Merus (MRUS) 6-K 19 Aug 19 2019 Q2 Unaudited Condensed Consolidated Statement of Financial Position Financial data

Document and Entity Information

Document and Entity Information	6 Months Ended
	Jun. 30, 2019
Document and entity information [abstract]
Document Type	6-K
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Registrant Name	Merus N.V.
Entity Central Index Key	0001651311
Current Fiscal Year End Date	--12-31

Unaudited Condensed Consolidate

Unaudited Condensed Consolidated Statement of Financial Position - EUR (€) € in Thousands	Jun. 30, 2019	Dec. 31, 2018
Non-current assets
Property, plant and equipment, net	€ 2,585	€ 2,420
Lease right-of-use assets	6,069
Intangible assets, net	2,351	2,445
Non-current investments	12,319	16,945
Other assets	742	1,075
Non-current assets	24,066	22,885
Current assets
Taxes and social security assets	978
Trade and other receivables	8,295	7,032
Current investments	35,560	44,855
Cash and cash equivalents	131,993	143,747
Current assets	176,826	195,634
Total assets	200,892	218,519
Shareholders' equity
Issued and paid-in capital	2,105	2,102
Share premium account	264,878	264,854
Accumulated loss	(190,214)	(175,085)
Total shareholders' equity	76,769	91,871
Non-current liabilities
Deferred revenue	89,666	97,675
Other liabilities	4,705
Non-current liabilities	94,371	97,675
Current liabilities
Trade payables	2,666	3,819
Taxes and social security liabilities	128	256
Deferred revenue	17,208	16,934
Other liabilities and accruals	9,750	7,964
Current liabilities	29,752	28,973
Total liabilities	124,123	126,648
Total shareholders' equity and liabilities	€ 200,892	€ 218,519

Unaudited Condensed Consolida_2

Unaudited Condensed Consolidated Statement of Profit or Loss and Comprehensive Loss - EUR (€) € in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses from railroad and related business [abstract]
Revenue		€ 5,579	€ 6,543	€ 13,281	€ 16,464
Research and development costs		(9,984)	(12,523)	(20,355)	(22,821)
Management and administration costs		(3,119)	(2,639)	(5,055)	(5,491)
Other expenses		(3,743)	(3,297)	(7,747)	(5,983)
Total operating expenses		(16,846)	(18,459)	(33,157)	(34,295)
Operating result		(11,267)	(11,916)	(19,876)	(17,831)
Finance income		476	7,411	1,899	4,945
Finance cost		(1,144)	(1)	(96)	(1)
Net finance income (expense)		(668)	7,410	1,803	4,944
Result before taxation		(11,935)	(4,506)	(18,073)	(12,887)
Income tax expense		(54)	(87)	(120)	(139)
Result after taxation		(11,989)	(4,593)	(18,193)	(13,026)
Items that are or may be reclassified subsequently to profit or loss
Exchange differences from the translation of foreign operations		(17)	36	6	21
Total other comprehensive income for the period		(17)	36	6	21
Total comprehensive loss for the period		€ (12,006)	€ (4,557)	€ (18,187)	€ (13,005)
Loss per share - basic and diluted	[1]	€ (0.51)	€ (0.20)	€ (0.78)	€ (0.60)
Weighted average shares outstanding - basic and diluted	[1]	23,387,841	22,628,611	23,380,488	21,809,950
[1]	For the periods included in these financial statements, share options were excluded from the diluted loss per share calculation as the Company was in a loss position in each period presented above. As a result, basic and diluted loss per share are equal.

Unaudited Condensed Consolida_3

Unaudited Condensed Consolidated Statement of Changes in Shareholders' Equity - EUR (€) € in Thousands	Total	Issued capital [member]Common share capital [member]	Share premium [member]Common share premium [member]	Accumulated loss [member]
Beginning balance (Previously stated [member]) at Dec. 31, 2017	€ 56,592	€ 1,749	€ 213,618	€ (158,775)
Result after taxation for the period	(13,026)			(13,026)
Other comprehensive income	21			21
Total comprehensive loss for the period	(13,005)			(13,005)
Transactions with owners of the Company:
Issuance of shares (net)	44,731	288	44,443
Equity settled share-based payments	4,554			4,554
Total contributions by owners	49,285	288	44,443	4,554
Ending balance at Jun. 30, 2018	92,872	2,037	258,061	(167,226)
Beginning balance at Dec. 31, 2018	91,871	2,102	264,854	(175,085)
Result after taxation for the period	(18,193)			(18,193)
Other comprehensive income	6			6
Total comprehensive loss for the period	(18,187)			(18,187)
Transactions with owners of the Company:
Issuance of shares (net)	27	3	24
Equity settled share-based payments	3,058			3,058
Total contributions by owners	3,085	3	24	3,058
Ending balance at Jun. 30, 2019	€ 76,769	€ 2,105	€ 264,878	€ (190,214)

Unaudited Condensed Consolida_4

Unaudited Condensed Consolidated Statement of Cash Flows - EUR (€) € in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Result after taxation	€ (18,193)	€ (13,026)
Adjustments for:
Unrealized foreign exchange results	(698)	(3,648)
Depreciation and amortization	1,049	218
Share-based payment expenses	3,058	4,554
Other non-cash adjustments	(1,085)	(531)
Cash flows from (used in) operations before changes in working capital	(15,869)	(12,433)
Changes in operating assets and liabilities:
Taxes and social security assets	(978)
Trade and other receivables	(1,164)	(959)
Other assets	333	(38)
Trade payables	(1,153)	2,307
Other liabilities and accruals	882	2,233
Deferred revenue	(7,735)	(5,796)
Taxes and social security liabilities	(128)	(143)
Cash used in operations	(25,812)	(14,829)
Interest paid	(96)	(1)
Taxes paid	(171)	(302)
Net cash used in operating activities	(26,079)	(15,132)
Cash flow from investing activities
Purchases of investments	(30,551)	(29,560)
Proceeds from investment maturities	45,114	18,931
Purchases of intellectual property		(100)
Acquisition of property, plant and equipment	(889)	(624)
Interest received	929	602
Net cash provided by (used in) investing activities	14,603	(10,751)
Cash flow from financing activities
Proceeds from issuing shares, net of issuance costs	1	44,731
Proceeds from share option exercises	26
Payment of lease liabilities	(691)
Net cash provided by (used in) financing activities	(664)	44,731
Net increase (decrease) in cash and cash equivalents	(12,140)	18,848
Effects of exchange rate changes on cash and cash equivalents	386	1,801
Cash and cash equivalents as at beginning of period	143,747	149,678
Cash and cash equivalents as at end of period	131,993	170,327
Changes in accrued capital expenditures	€ (363)	€ 271

General information

General information	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
General information	1. General information Nature of Business Merus N.V. is a clinical-stage immuno-oncology company developing innovative bispecific antibody therapeutics, headquartered in Utrecht, the Netherlands. Merus US, Inc. is a wholly-owned subsidiary of Merus N.V. located at 139 Main St., Cambridge, Massachusetts, United States. These condensed consolidated interim financial statements as at and for the three and six months ended June 30, 2019, comprise Merus N.V. and Merus US, Inc. (collectively, the “Company”). Since inception, the Company has generated an accumulated loss of €190.1 million as of June 30, 2019. The Company expects to continue to incur significant expenses and operating losses for the foreseeable future as its bispecific antibody candidates advance through discovery, preclinical development and clinical trials and as it seeks regulatory approval and pursues commercialization of any approved bispecific 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 with third parties and business development opportunities. 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. Therefore, the financial statements of the Company have been prepared on the basis of the going concern assumption. Based on the Company’s current operating plan, it expects that its existing cash and cash equivalents of €132.0 million and investments of €47.9 million as of June 30, 2019 will be sufficient to fund its operations into the second quarter of 2021. Equity Offering On February 13, 2018, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) with the purchasers named therein (the “Investors”). Pursuant to the Purchase Agreement, the Company agreed to sell an aggregate of 3,099,997 of its common shares, nominal value €0.09 per share, to the Investors at a purchase price equal to $18.0 per share (the “Private Placement”). The Purchase Agreement contained customary representations and warranties from the Company and the Investors and customary closing conditions. On February 15, 2018, the Company completed the sale under the Private Placement and received aggregate gross proceeds of approximately $55.8 million, or €44.8 million.

Significant accounting policies

Significant accounting policies	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Significant accounting policies	2. Significant accounting policies There have been no significant changes to the Company’s accounting policies that were previously disclosed in its Annual Report on Form 20-F Basis of Presentation These unaudited interim condensed consolidated financial statements (the “interim financial statements”) have been prepared in accordance with International Accounting Standard (“IAS”) 34, Interim Financial Reporting Form 20-F Use of Estimates The preparation of financial statements in conformity with IFRS requires the use of certain critical accounting estimates. It also requires management to exercise its judgment in the process of applying the Company’s accounting policies. The areas involving a higher degree of judgment or complexity or areas where assumptions and estimates are significant to these interim financial statements are disclosed in Note 4. The results of operations for the three and six months ended June 30, 2019 are not necessarily indicative of operations to be expected for the full fiscal year ending December 31, 2019. Foreign Currency Transactions 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”). The interim financial statements are presented in euros, which is Merus N.V.’s functional currency. The functional currency of Merus US, Inc. is the U.S. dollar. All amounts are rounded to the nearest thousand euros, except where otherwise indicated. Seasonality The Company’s financial results have varied substantially, and are expected to continue to vary, from period to period. The Company believes that its ordinary activities are not linked to any particular seasonal factors. Segment Reporting The Company operates in one reportable segment, which comprises the discovery and development of innovative bispecific therapeutics. Cash and Cash Equivalents For the purpose of presentation in the unaudited condensed consolidated Revenue Recognition The Company accounts for revenue in accordance with IFRS 15, Revenue from Contracts with Customers The terms of the contracts within the scope of IFRS 15 may contain multiple promised goods and services, which often include license rights to certain of the Company’s product candidates and research and development (“R&D”) activities. Payments under such agreements include: (i) upfront nonrefundable license fees; (ii) payments for R&D services performed by the Company, including reimbursement for certain external costs; (iii) payments based upon the achievement of certain development, regulatory and commercial milestones; and (iv) royalties on net product sales, if any. Under IFRS 15, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the Company expects to receive in exchange for those goods or services. The Company recognizes revenue following the five-step model prescribed under IFRS 15: (i) identification of the contract(s) with the customer; (ii) identification of the performance obligations; (iii) determination of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations in the contract; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. In order to account for contracts with customers, the Company identifies the promised goods or services in the contract and evaluates whether such promised goods or services represent performance obligations. The Company accounts for those components as separate performance obligations when the following criteria are met: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer, and (ii) the Company’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. This evaluation requires subjective determinations and requires the Company to make judgments about the promised goods and services and whether such goods and services are separable from the other aspects of the contractual relationship. In determining the performance obligations, the Company evaluates certain criteria, including whether the promised good or service is capable of being distinct and whether such good or service is distinct within the context of the contract, based on consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research, manufacturing and commercialization capabilities of the customer; the availability of research and manufacturing expertise in the general marketplace; and the level of integration, interrelation, and interdependence among the promises to transfer goods or services. The transaction price is allocated among the performance obligations using the relative selling price method and the applicable revenue recognition criteria are applied to each of the separate performance obligations. At contract inception, the Company determines the standalone selling price for each performance obligation identified in the contract. If an observable price of the promised good or service sold separately is not readily available, the Company utilizes assumptions that require judgment to estimate the standalone selling price, which may include development timelines, probabilities of technical and regulatory success, reimbursement rates for personnel costs, forecasted revenues, potential limitations to the selling price of the product, expected technological life of the product and discount rates. Upfront License Payments If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are not distinct and bundled with other performance obligations, 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 from the combined performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestones At the inception of each arrangement that includes pre-commercial milestone cumulative catch-up Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and where 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 royalty revenue. R&D Cost Reimbursement R&D cost reimbursement revenue, which is typically related to reimbursements from customers for the Company’s performance of R&D services under the respective agreements, is recognized on the basis of labor hours valued at a contractually agreed rate. R&D cost reimbursement revenue also includes reimbursements for related out-of-pocket expenses The Company typically acts as the principal under such arrangements and, therefore, records these reimbursements on a gross basis. The impact of the new revenue standard IFRS 15 was also assessed for the instances under the ONO Pharmaceutical Co., Ltd. (“ONO”) research and license agreement where the Company acts as an agent. The Company concluded that no control was obtained for these pass-through arrangements to reimburse costs under the ONO research and license agreement and as such the cost reimbursements were netted in R&D instead of being recognized as revenue. C osts of Obtaining a Contract with a Customer The Company capitalizes the incremental costs of obtaining a contract with a customer if it expects to recover those costs. To date, the Company has not capitalized any incremental costs for obtaining a contract. 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. Leases Effective January 1, 2019, the Company adopted IFRS 16, Leases right-of-use IFRS 16 introduces a single lessee accounting model and requires a lessee to recognize assets and liabilities for all leases with a term of more than 12 months, unless the underlying asset is of low value. A lessee is required to recognize a right-of-use Determining whether an Arrangement Contains a Lease At inception of an arrangement, the Company determines whether the arrangement conveys the right to control the use of an identified asset for a period in exchange for consideration, in which case the arrangement is, or contains, a lease. At inception or on reassessment of an arrangement that contains a lease, the Company allocates the consideration in the arrangement to each lease component on the basis of the relative stand-alone price of the lease component and the aggregate stand-alone price of the non-lease non-real non-lease non-lease Lease Assets and Lease Liabilities The Company recognizes a right-of-use The lease liability is initially measured at the present value of outstanding lease payments, discounted using the interest rate implicit in the lease or, if that rate cannot be readily determined, the Company’s incremental borrowing rate. The lease liability is measured at amortized cost using the effective interest method and is remeasured when there is a change in future lease payments arising from a change in an index or rate. A corresponding adjustment is made to the carrying amount of the lease asset. Interest expense related to the Company’s lease liabilities is recognized as a finance expense in the condensed consolidated statement of profit or loss and comprehensive loss. Short-Term Leases and Low Value-Leases The Company has elected not to recognize lease assets and lease liabilities for short-term leases (leases with a term of 12 months or less) and leases of low-value

Recently Issued or Adopted Inte

Recently Issued or Adopted International Financial Reporting Standards	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Recently Issued or Adopted International Financial Reporting Standards	3. Recently Issued or Adopted International Financial Reporting Standards Except as otherwise indicated, the accounting policies adopted in the preparation of these interim financial statements are consistent with those applied in the preparation of the Company’s consolidated financial statements for the year ended December 31, 2018. Newly Adopted International Financial Reporting Standards IFRS 16, Leases In January 2016, the IASB issued IFRS 16, which supersedes existing lease guidance. Prior to the adoption of IFRS 16, the Company classified leases as operating or finance leases based on its assessment of whether the lease transferred substantially all of the risks and rewards of ownership. A lease asset and lease liability were recognized for those leases classified as finance leases. Operating leases were not recognized in the Company’s statement of financial position. IFRS 16 established a right-of-use The Company adopted IFRS 16 on January 1, 2019, using a modified retrospective transition approach applied to leases existing as of, or entered into after, January 1, 2019. The Company elected to utilize the package of practical expedients available for expired or existing contracts, which allowed the Company to carryforward historical assessments of whether contracts are or contain leases, lease classification and accounting for initial direct costs. In addition, the Company elected the practical expedients related to the recognition exemption for short-term leases and low-value leases. low-value

Use of Estimates, Judgments and

Use of Estimates, Judgments and Assumptions	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Use of Estimates, Judgments and Assumptions	4. Use of Estimates, Judgments and Assumptions In the application of the Company’s accounting policies, management is required to make judgments, estimates and assumptions that affect the reported amounts of assets, liabilities, income and expenses that are not readily apparent from other sources. The estimates and associated assumptions are based on historical experience and other factors that are considered to be relevant. Actual results may differ from these estimates. Estimates and underlying assumptions are reviewed on an ongoing basis. Revisions to accounting estimates are recognized prospectively. The following are the critical judgments and assumptions that management has made in the process of applying the Company’s accounting policies and that have the most significant effect on the amounts recognized in the interim consolidated financial statements. Equity settled share-based payments Share options granted to employees, consultants and directors are measured at the grant date fair value of the equity instruments granted. The grant date fair value is determined through the use of an option-pricing model considering the following variables: (a) the exercise price of the option; (b) the expected life of the option; (c) the current value of the underlying shares; (d) the expected volatility of the share price; (e) the dividends expected on the shares; (f) the risk-free interest rate for the life of the option; and (g) the expected share option forfeitures. The estimated fair value of each share option granted is determined utilizing the Hull & White option pricing model, which considers the terms and conditions attached to the grants made and is reflective of expected exercise behavior. Because the Company’s shares have been publicly traded for a relatively short amount of time, the expected volatility is set by also giving weight to the historic share price volatility of a set of peer companies. As a proxy for the risk-free rate, the continuous yield on U.S. Treasury Bills with a term to maturity comparable to the expected life of the options, as published by the U.S. Department of Treasury, is applied. The result of the share option valuations and the related compensation expense that is recognized for the respective vesting periods during which services are received are dependent on the model and input parameters used. Even though management considers the fair values reasonable and defensible based on the methodologies applied and the information available, others might derive a different fair value for the Company’s share options. These assumptions and estimates are further discussed in Note 10 to the interim financial statements. Capitalization of development costs The criteria for capitalization of development costs have been considered by management and determined not to have been met through June 30, 2019. Therefore, all development expenditures relating to internally generated intangible assets during the six months ended June 30, 2019 were expensed as incurred. Income taxes As of June 30, 2019, deferred tax assets have not been recognized in respect of tax losses and deductible temporary differences. In November 2018, the Dutch tax authorities confirmed that the $120.0 million upfront license fee received from Incyte Corporation (“Incyte”) can be fully recognized in 2017 for Dutch corporate income tax purposes, which resulted in a significant reduction of the Company’s tax loss carry-forwards. The treatment of upfront license fees received is consistently applied by the Company for Dutch corporate income tax purposes. There will be no impact on the Company’s consolidated statements of financial position or consolidated statement of profit or loss and comprehensive loss as no deferred tax asset was recognized. Therefore, at the balance sheet date, there is no convincing evidence that sufficient taxable profit will be available against which the tax losses and deductible temporary differences can be utilized. Merus US, Inc., which is incorporated in the U.S. in the State of Delaware, is subject to statutory U.S. Federal corporate income taxes and state income taxes for Massachusetts. Current year income tax expense was attributable entirely to Merus US, Inc., which provides general management services and strategic advisory services to the Company. Corporate income tax expenses were €0.1 million for the three and six months ended June 30, 2019, as compared to €0.1 million for the three and six months ended June 30, 2018. Revenue recognition Pursuant to the Company’s research, collaboration and license agreements with ONO, Incyte, Jiangsu Simcere Pharmaceutical Co. Ltd. (“Simcere”) and Betta Pharmaceuticals Co. Ltd. (“Betta”), the Company has received upfront nonrefundable payments and milestone payments for certain rights granted under the respective agreements. The applicable period over which to recognize these upfront or milestone payments requires significant judgment and was impacted by the adoption of IFRS 15 (See Note 8). Accrual of R&D expenses R&D expenses represent costs that primarily include: (i) payroll and related costs (including share-based payment expenses) associated with R&D personnel; (ii) costs related to clinical trials and preclinical testing of the Company’s technologies under development; (iii) costs to develop product candidates, including raw materials and supplies, product testing, depreciation, and facility related expenses; (iv) expenses for research services provided by universities and contract laboratories; and (v) other R&D expenses. R&D expenses are recognized in the consolidated statement of profit or loss and comprehensive loss as incurred and have no alternative future uses. As part of the process of preparing its consolidated financial statements, the Company is required to estimate certain of its R&D expenses, including estimates of third-party contract costs relating to preclinical studies and clinical trial activities and related contract manufacturing expenses. This process involves reviewing open contracts and purchase orders, communicating with R&D personnel to identify services that have been performed for the Company and estimating the level of service performed and the associated cost incurred for the service when the Company has not yet been invoiced or otherwise notified of the actual cost. The majority of the Company’s service providers invoice monthly in arrears for services performed or when contractual milestones are met. The Company makes estimates of its R&D expenses as of each reporting date in its consolidated financial statements based on facts and circumstances known to it at that time. The Company periodically confirms the accuracy of its estimates with the service providers to gauge the reasonableness of its estimates. Differences between actual and estimated expenses recorded have not been material and are adjusted for in the period in which they become known.

Investments

Investments	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Investments	5. Investments The Company classifies and accounts for its investments at amortized cost in accordance with IFRS 9, Financial Instruments The Company’s investments include investments in commercial paper, debt securities issued by several public corporations and the U.S. Treasury. Current investments include investments with a maturity date of greater than three months at the date of settlement. Investments with a maturity of 12 months or more from the original investment date are classified as non-current. Investments as of June 30, 2019 and December 31, 2018 consisted of the following: Balance as per June 30, December 31, (euros in thousands) Commercial paper 13,929 22,208 U.S. Treasury securities 2,411 6,733 Corporate fixed income bonds 17,465 14,185 Agency bonds 1,755 1,729 Current investments 35,560 44,855 Corporate fixed income bonds 12,319 16,945 Non-current 12,319 16,945 Total investments 47,879 61,800 During the six months ended June 30, 2019, the Company purchased investments totaling €30.6 million, which are held and denominated in U.S. dollars, and received proceeds of €45.1 million relating to investment maturities. As a result of the fluctuation in foreign currency between the euro and U.S. dollar, the Company recorded foreign currency exchange gains of approximately €0.4 million and foreign currency exchange losses of approximately €0.7 million as a component of finance income for the three and six months ended June 30, 2019, respectively.

Trade and Other Receivables

Trade and Other Receivables	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Trade and Other Receivables	6. Trade and Other Receivables All receivables as included in the following table are short-term and due within one year. Balance as per June 30, December 31, (euros in thousands) Trade receivables 1,393 2,690 Unbilled receivables 72 236 VAT receivable 684 891 Prepaid expenses 4,526 2,783 Prepaid pension costs 631 — Interest receivable 312 213 Other receivables 677 219 8,295 7,032 Trade and unbilled receivables relate primarily to invoicing for cost reimbursements relating to the Incyte collaboration and license agreement, ONO research and license agreements and Simcere research and license agreement. VAT receivable relates to a value added tax receivable from the Dutch tax authorities based on the tax application for the second quarter of 2019. The Company is evaluating if the benefits of claiming foreign VAT are favorable compared to the related costs and expects to finalize its assessment and reach a conclusion in 2019. Prepaid expenses consist of expenses that were paid but are related to activities taking place in subsequent periods. Tax and Social Security Liabilities The WBSO ( afdrachtvermindering speur- en ontwikkelingswerk

Other Liabilities and Accruals

Other Liabilities and Accruals	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Other Liabilities and Accruals	7. Other Liabilities and Accruals All amounts are short-term and payable within one year. Balance as per June 30, December 31, (euros in thousands) Audit fees 70 167 Personnel-related 405 560 Accrued bonus 928 1,523 Accrued R&D costs 4,758 4,409 Lease liabilities 1,432 — IP legal fees 258 212 Subsidy advances received 151 42 Other accruals 1,748 1,051 9,750 7,964 Accrued R&D costs relate to third-party contract costs for preclinical studies and clinical trial activities and related contract manufacturing expenses. Accrued bonuses relate to employee bonuses for the financial year 2019, which are expected to be paid out in February 2020. Financial year 2018 bonuses were paid in March 2019. IP legal fees relate to legal cost incurred to obtain, maintain and defend the Company’s intellectual property, including patent applications, patents and trademarks related thereto. Lease liabilities relate to the current portion of lease liabilities recognized under IFRS 16. See Note 3 and Note 9 for further details. Subsidy advances received relate to active grants where the Company has received cash in excess of allowances, which is required to be repaid or recognized as grant revenue when the relevant reimbursable costs are incurred as services are performed.

Deferred Revenue

Deferred Revenue	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Deferred Revenue	8. Deferred Revenue Deferred revenue as of June 30, 2019 and December 31, 2018 consisted of the following: Balance as per June 30, December 31, (euros in thousands) Deferred revenue – current portion 17,208 16,934 Deferred revenue 89,666 97,675 106,874 114,609 Of the total deferred revenue balance at June 30, 2019, €104.7 million related to the Incyte collaboration and license agreement and a share subscription agreement (the “Incyte share subscription agreement”) entered into by the Company with Incyte on December 20, 2016 (together, the “Incyte Agreements”), €1.6 million related to the collaboration and license agreement entered into by the Company with Simcere on January 8, 2018 (the “Simcere collaboration and license agreement”) and €0.6 million related to the collaboration and license agreement entered into by the Company with Betta on December 10, 2018 (the “Betta collaboration and license agreement”). Of the total deferred revenue balance at December 31, 2018, €112.6 million related to the Incyte Agreements and €2.1 million related to the Simcere collaboration and license agreement. Under the Incyte collaboration and license agreement, Incyte agreed to pay the Company a $120.0 million, or €112.0 million, non-refundable upfront €112.0 million, non-refundable upfront As the Incyte share subscription agreement was denominated in a foreign currency (U.S. dollars) other than the Company’s functional currency (euro), the Company determined that the freestanding forward contract to sell its own shares at a future date, to which the Company became committed on December 20, 2016, did not qualify as equity and thus a freestanding forward contract (derivative asset) was recognized in the Company’s consolidated statement of financial position. The difference between the purchase price of $25.00 per common share in the Incyte share subscription agreement and the market price of the Company’s common shares on December 20, 2016 was considered to be part of the consideration received under the Incyte Agreements. As a result, on December 20, 2016, the Company recorded a liability (deferred revenue) of $32.6 million, or €31.4 million, in its consolidated statement of financial position for the same amount as the fair value of the freestanding forward contract (derivative asset). The deferred revenue liability is not remeasured subsequent to the initial recognition and is accounted for in the same manner as the non-refundable upfront The Company’s fixed consideration under the Incyte Agreements is $152.6 million, or €143.4 million, consisting of the $120.0 million, or €112.0 million, non-refundable Under the Simcere collaboration and license agreement, the Company agreed to grant Simcere an exclusive license to develop and commercialize in China three bispecific antibodies to be produced by the Company utilizing the Company’s Biclonics ® upfront, non-refundable payment The Company amortizes the upfront payment to revenue over time based on the estimated duration of each research program. As of June 30, 2019, the first and second research programs had commenced. For the three and six months ended June 30, 2019, the Company recognized revenue of €0.2 million and €0.5 million, respectively, relating to these two programs for the amortization of upfront and milestone payments. The third research program had not commenced as of June 30, 2019. Accordingly, no revenue has been recognized related to that research program. On March 14, 2018, the Company entered into a second contract research and license agreement with ONO (the “second ONO research and license agreement”). Pursuant to an exclusive option granted to ONO in the ONO research and license agreement, ONO exercised its option to enter into the second ONO research and license agreement. 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 ® Under the terms of the agreement, ONO identifies and selects the licensed bispecific antibodies for which it is responsible for conducting further non-clinical and clinical ONO agreed to pay the Company an upfront, non-refundable payment of Under the Betta collaboration and license agreement, the Company granted Betta an exclusive license to develop and commercialize in China MCLA-129, a ® ® IND-enabling In addition to a non-refundable upfront The Company identified a single combined performance obligation, which includes a license to MCLA-129 and the IND-enabling studies. Betta is eligible to receive from the Company an aggregate of $12.0 million, or €10.5 million, in milestone payments contingent upon the Company achieving certain specified development and commercial goals and is eligible to receive tiered royalty payments of net sales outside of China.

Leases

Leases	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Leases	9. Leases Merus N.V. leases its corporate headquarters under an agreement term of five years, which expires in the fourth quarter of 2021. If the lease is not terminated by Merus N.V., it will be automatically renewed for a period of two years. On May 1, 2018, Merus N.V. leased additional space to expand its corporate headquarters under a separate agreement. Under the terms of the new agreement, the term began on May 1, 2018 and expires in the fourth quarter of 2021. On January 1, 2019, the Company adopted IFRS 16 using a modified retrospective transition approach applied to leases existing as of, or entered into after, January 1, 2019 (see Note 3). The Company applied the standard only to leases that were previously identified as leases under existing lease guidance. Adoption of the new standard resulted in the recognition of lease assets (lease right-of-use non-current In March 2019, Merus US Inc. entered into a lease agreement for office space in Cambridge, Massachusetts. The lease commenced in the second quarter of 2019 and has a term of seven years. The Company recognized a lease asset of $4.3 million, or €3.8 million, and a lease liability of $4.3 million, or €3.8 million, on the condensed consolidated statement of financial position as of the lease commencement date. To measure the leas liability, the Company discounted the outstanding lease payments using its incremental borrowing rate at the lease commencement date of 4.50%.

Shareholders' Equity

Shareholders' Equity	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Shareholders' Equity	10. Shareholders’ Equity Private Placement of Common Shares On February 13, 2018, the Company entered into the Purchase Agreement. Pursuant to the Purchase Agreement, the Company agreed to sell an aggregate of 3,099,997 of its common shares to the Investors at a purchase price equal to $18.00 per share. The Purchase Agreement contains customary representations and warranties from the Company and the Investors and customary closing conditions. On February 15, 2018, the Company completed the sale under the Private Placement and received gross proceeds of approximately $55.8 million, or €44.8 million. Share Subscription Agreement with Regeneron On December 20, 2018, the Company entered into a share subscription agreement (the “Regeneron Subscription Agreement”) with Regeneron Pharmaceuticals, Inc. (“Regeneron”). Pursuant to the Regeneron Subscription Agreement, the Company agreed to sell an aggregate of 600,000 of its common shares to Regeneron at a purchase price equal to $25.00 per share. On December 21, 2018, the Company completed the sale under the Regeneron Subscription Agreement and received gross proceeds of $15.0 million, or €13.1 million. Accordingly, the Company recorded the common shares issued at the fair value of the underlying securities on the date of issuance. The difference between the total proceeds received of $15.0 million, or €13.1 million, and the aggregate value of common shares issued of $6.9 million, or €6.0 million, was recorded as a gain on litigation settlement (see Note 12) of $8.1 million, or €7.1 million, during the year ended December 31, 2018. Issued and paid-in All issued shares have been fully paid in cash. Common shares At June 30, 2019 and 2018, a total of 23,393,287 and 22,632,800 common shares, respectively, were issued and fully paid in cash. The following is a tabular reconciliation of common shares outstanding for the six months ended June 30, 2019 and 2018. Six months ended June 30, 2019 2018 Common Shares outstanding at January 1, 23,358,977 19,429,848 Issued for cash — 3,099,997 Exercise of common share options 9,980 34,041 Vesting of RSUs 24,330 68,914 Common shares outstanding at June 30, 23,393,287 22,632,800 Share Premium Reserve The share premium reserve relates to amounts contributed by shareholders at the issue of shares in excess of the par value of the shares issued. All share premium can be considered as free share premium as referred to in the Netherlands Income tax act. Share-based Payment Arrangements Share-based payment expenses included in personnel expenses were €3.1 million and €4.6 million during the six months ended June 30, 2019 and 2018, respectively. For details on the related share-based payment expenses recognized as employee benefit expenses see Note 13. In June 2016, the Company established the 2016 Incentive Award Plan (the “2016 Plan”). Options granted under the 2016 Plan are exercisable once vested and vest in installments over a four-year period from the grant date. Twenty-five percent of the options 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 by the option holder thereafter, such that 100% of the options shall become vested on the fourth anniversary of the vesting commencement date. Options will lapse on the tenth anniversary of the date of grant. The Restricted Share Units (“RSUs”) granted under the 2016 Plan also vest in installments over a four-year period from the grant date. Each RSU represents the right to receive one common share. As stated in the 2016 Plan, the Company has established the Non-Executive non-executive Non-Executive Share-based payment expenses are recognized for each subsequent award that a non-executive During the six months ended June 30, 2019, the Company granted options to purchase 1,009,671 common shares with a grant date fair value of €10.3 million to employees under the 2016 Plan. Pursuant to the “evergreen” provisions of the 2016 Plan, the number of common shares authorized for issuance under the plan automatically increased by 934,359 common shares to 1,469,785 common shares effective January 1, 2019. Measurement of fair values of the equity-settled share-based payment arrangements The fair value of the share options granted to employees and the Board of Directors has been measured using the binomial option pricing model. Share-based compensation is recognized as an expense based on the grant date fair value over the vesting period in accordance with each separate vesting tranche of the award granted, taking into consideration actual and expected forfeitures at each reporting date and at the respective vesting dates. Service and non-market performance The inputs used in the measurement of the fair values and the related fair values at the grant dates for the options granted during the six months ended June 30, 2019 were: Key Management euros ) All Other Personnel euros ) Fair value at grant date 6.07 – 7.60 6.15 – 8.62 Share price at grant date 9.83 – 12.49 9.83 – 14.19 Exercise price 9.83 – 12.49 9.83 – 14.19 Expected volatility (weighted-average) 87.58 % 87.11 % Contractual life 10 years 10 years Expected dividends — % — % Risk-free interest rate (based on government bonds) 2.13%—2.74 % 2.02%—2.65 % Reconciliation of outstanding share options The number of share options and the weighted average exercise prices of share options granted were as follows for the six months ended June 30, 2019: Weighted average euros ) Number of Outstanding at January 1, 2019 14.62 2,633,039 Forfeited during the six months 14.07 (223,631 ) Expired during the six months 15.95 (126,589 ) Exercised during the six months 11.02 (9,980 ) Granted during the six months 10.23 1,009,671 Outstanding at June 30, 2019 13.27 3,282,510 Exercisable at June 30, 2019 13.34 1,533,094 The options outstanding at June 30, 2019, had an exercise price in the range of €1.93 to €27.47 and a weighted-average remaining contractual life of 7.3 years. The weighted-average share price at the date of exercise for share options exercised during the six months ended June 30, 2019 was €11.02. There were 3,282,510 outstanding share options at June 30, 2019, with a weighted average exercise price of €13.27. The number of options outstanding by group of employees as of June 30, 2019, was as follows: Group of employees entitled June 30, 2019 Key management personnel 2,580,281 All other employees 702,229 Total 3,282,510 During the six months ended June 30, 2019, the Company did not grant any new RSUs. The following table summarizes the Company’s RSU activity for the six months ended June 30, 2019: Weighted average euros ) Number of Outstanding at January 1, 2019 20.03 101,302 Forfeited during the six months — — Vested during the six months 20.03 (24,330 ) Granted during the six months — — Outstanding at June 30, 2019 — 76,972

Revenue

Revenue	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Revenue	11. Revenue Revenue is recognized at the amount to which the Company expects to be entitled for the transfer of promised goods or services to customers. Disaggregation of Revenue The Company’s revenues are generated entirely in the Netherlands. In the following table, revenue is disaggregated by primary source of revenue as follows: Three months ended Six months ended June 30, June 30, June 30, June 30 (euros in thousands) (euros in thousands) Upfront payment amortization 4,231 4,250 8,436 9,087 R&D cost reimbursement 1,383 2,040 3,806 4,556 Milestone revenue 74 139 1,148 2,639 Revenue from contracts with customers 5,688 6,429 13,390 16,282 Income (expense) from grants on research projects (109 ) 114 (109 ) 182 5,579 6,543 13,281 16,464 For the three and six months ended June 30, 2019, the Company recognized amortization of €4.0 million and €7.9 million on upfront payments related to the Incyte collaboration and license agreement, respectively, €0.1 million and €0.3 million on upfront payments related to the Simcere collaboration and license agreement, respectively, and €0.1 million and €0.2 million on the upfront payment related to the Betta collaboration and license agreement, respectively. For the three and six months ended June 30, 2018, the Company recognized amortization of €4.0 million and €7.9 million on upfront payments related to the Incyte collaboration and license agreement, respectively, €0.2 million and €1.1 million on upfront payments related to the ONO research and license agreement, respectively, and €0.1 million and €0.1 million on upfront payments related to the Simcere collaboration and license agreement, respectively. For the three and six months ended June 30, 2019, the Company recognized €1.4 million and €3.6 million of cost reimbursements in support of the Incyte collaboration and license agreement with Incyte, respectively, zero and €0.1 million of cost reimbursements in support of the research and license agreements with ONO, respectively, and less than €0.1 million and €0.1 million of cost reimbursements in support of the Betta collaboration, research and license agreement, respectively. For the three and six months ended June 30, 2018, the Company recognized €2.0 million and €4.3 million of cost reimbursements in support of the Incyte collaboration and license agreements, respectively, and €0.1 million and €0.2 million of cost reimbursements in support of the research and license agreements with ONO, respectively. Milestone revenue consists of milestone payment amortization and research milestones achieved in support of the agreements with ONO and Simcere. For the three and six months ended June 30, 2019 the Company recognized an aggregate of zero and €1.0 million in research milestones under the research and license agreements with ONO, respectively, and €0.1 million and €0.1 million in research milestone payment amortization under the Simcere collaboration and license agreement, respectively. The Company did not recognize any revenue relating to research milestones under the Betta collaboration and license agreement for the three and six months ended June 30, 2019. For the three and six months ended June 30, 2018 the Company recognized an aggregate of zero and €2.5 million in research milestones under the research and license agreement with ONO, respectively, and €0.1 million and €0.1 million in research milestone payment amortization under the Simcere collaboration and license agreement, respectively. The Company has been awarded grants consisting of cash allowances for specific R&D projects. The unconditional receipt of the grant allowances is dependent on the final review of the reporting provided by the Company at the end of the contract term. During the second quarter of 2019, the Company received notification from the Netherlands Enterprise Agency that €0.1 million of declared costs previously recognized as grant revenue were not reimbursable. Therefore, the Company recognized €0.1 million as a reduction in grant income for the three and six months ended June 30, 2019, compared to €0.1 million and €0.2 million in grant income for the three and six months ended June 30, 2018, respectively. As of August 2018, all grants awarded were completed. Contract Balances A trade receivable is recorded when the Company satisfies a performance obligation by transferring a promised good or service and has earned the unconditional right to consideration from its customer. Trade receivables relate to invoicing for cost reimbursements, upfront payments and research milestones achieved in support of the Company’s agreements with Incyte, ONO, Simcere and Betta. Payment terms relating to receivables with Incyte, ONO and Simcere are 30 days and payment terms relating to receivables with Betta are 60 days. A contract asset is recorded when the Company satisfies a performance obligation by transferring a promised good or service and has earned the right to consideration from its customer. These assets represent a conditional right to consideration. Contract assets relate to unbilled amounts for cost reimbursements in support of the Company’s research and license agreements with Incyte and Betta. A contract liability is recorded when consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services under the terms of the contract. Contract liabilities are recognized as revenue as control of the products or services is transferred to the customer and all revenue recognition criteria have been met. Contract liabilities relate to upfront payments received related to the Incyte collaboration and license agreement, Simcere research and license agreement and Betta collaboration and license agreement (See Note 8). The following table presents changes in the Company’s trade receivables, contract assets and contract liabilities during the six months ended June 30, 2019: Balance at December 31, Additions Deductions Balance at June 30, (euros in thousands) Trade receivables Trade receivables 2,690 5,819 (7,116 ) 1,393 Total trade receivables 2,690 5,819 (7,116 ) 1,393 Contract assets Unbilled receivables 236 114 (278 ) 72 Total contract assets 236 114 (278 ) 72 Contract liabilities Deferred revenue 114,609 848 (8,583 ) 106,874 Total contract liabilities 114,609 848 (8,583 ) 106,874 For the six months ended June 30, 2019, additions to trade receivables are comprised of invoicing for cost reimbursements, upfront payments and research milestones, offset by cash receipts. For the six months ended June 30, 2019, deductions from deferred revenue were comprised of revenue recognized that was included in deferred revenue at the beginning of the period totaling €8.4 million and revenue recognized that was not included in deferred revenue at the beginning of the period totaling €0.2 million related to a payment received during the six months ended June 30, 2019.

Total Operating Expenses

Total Operating Expenses	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Total Operating Expenses	12. Total Operating Expenses R&D costs are comprised of allocated employee costs, the costs of materials and laboratory consumables, intellectual property and license costs and allocated other costs. The following table presents a breakdown of operating expenses: Three months ended June 30, Six months ended June 30, 2019 2018 2019 2018 (euros in thousands) Manufacturing costs 450 5,580 2,325 9,858 IP and license costs 585 492 876 844 Personnel related R&D 2,470 2,107 4,510 3,808 Other R&D costs 6,479 4,344 12,644 8,311 Total R&D costs 9,984 12,523 20,355 22,821 Management and administration costs 3,119 2,639 5,055 5,491 Litigation costs 59 552 123 849 Other operating expenses 3,684 2,745 7,624 5,134 Total other expenses 3,743 3,297 7,747 5,983 Total operating expenses 16,846 18,459 33,157 34,295 R&D costs were €9.9 million and €20.3 million for the three and six months ended June 30, 2019, respectively, as compared to €12.5 million and €22.8 million for the three and six months ended June 30, 2018, respectively. The decrease in R&D costs is primarily attributable to lower manufacturing costs, primarily for MCLA-128, MCLA-145, Other R&D costs consist mainly of laboratory supplies and depreciation expense related to R&D activities, which cannot be specifically allocated to a research project. A breakdown of other R&D costs is presented as follows: Three months ended June 30, Six months ended June 30, 2019 2018 2019 2018 ( euros in thousands ) Discovery and preclinical costs 2,055 1,078 4,175 1,763 Clinical costs 3,156 1,850 6,041 4,248 Other R&D costs 1,268 1,416 2,428 2,300 Total other R&D costs 6,479 4,344 12,644 8,311 Management and administration costs Management and administration costs were €3.1 million and €5.1 million for the three and six months ended June 30, 2019, respectively, as compared to €2.6 million and €5.5 million for the three and six months ended June 30, 2018, respectively. The increase in management and administration costs during the three months ended June 30, 2019 is primarily attributable to higher management and administration headcount and related costs, primarily offset by a decrease in share-based compensation expense. The decrease in management and administration costs during the six months ended June 30, 2019 is primarily attributable to a decrease in share-based compensation expense, partially offset by higher management and administration headcount and related costs. Litigation costs On April 5, 2018, an unnamed third party and Regeneron filed notices of opposition against the Company’s EP 2604625 patent, entitled “Generation of Binding Molecules,” in the European Patent Office. The notices asserted, as applicable, added subject matter, lack of novelty, lack of inventive step, and insufficiency. Regeneron withdrew from this proceeding in January 2019. On August 20, 2018, the Company timely responded to these submissions, and again in April 2019, with proceedings to be ongoing with respect to the unnamed third party. An opposition hearing was held June 2019 during which the patent was revoked. The Company intends to appeal this decision to the Technical Board of Appeals. As this opposition proceeding continues, the Company cannot be certain that the Company will ultimately prevail. The litigation and opposition related costs were €59,000 and €0.1 for the three and six months ended June 30, 2019, respectively, as compared to litigation and opposition costs incurred of €0.6 million and €0.8 million for the three and six months ended June 30, 2018, respectively, and are included in the condensed consolidated statement of profit or loss and comprehensive loss for the period. 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 other material legal proceedings. Other operating expenses Other operating expenses were €3.6 million and €7.6 million for the three and six months ended June 30, 2019, respectively, as compared to €2.7 million and €5.1 million for the three and six months ended June 30, 2018, respectively. The increase in other operating expenses is primarily attributable to an increase in consultant costs to support accounting operations and facilities-related expenses for the Cambridge, MA facility.

Employee Benefits

Employee Benefits	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Employee Benefits	13. Employee Benefits Details of the employee benefits are as follows: Three months ended Six months ended 2019 2018 2019 2018 (euros in thousands) Salaries and wages 3,454 2,876 6,476 5,505 WBSO subsidy (1,071 ) (733 ) (2,319 ) (1,900 ) Social security premiums 291 198 579 449 Health insurance 65 69 215 188 Pension costs 294 188 564 390 Share-based compensation 1,806 2,109 3,058 4,554 Other personnel expense 1,150 224 1,786 433 Total employee benefits expense 5,989 4,931 10,359 9,619 Share-based compensation expense recognized as employee benefit expenses was as follows: Three months ended Six months ended 2019 2018 2019 2018 (euros in thousands) R&D costs 715 714 1,482 1,525 Management and administration costs 919 1,343 1,255 2,852 Other expenses 172 52 321 177 1,806 2,109 3,058 4,554 Subsidies earned under the WBSO are deferred and recognized in the Company’s income statement as a reduction to labor costs over the period labor costs are expected to be incurred. The Company has recognized subsidies of €1.1 million and €2.3 million for the three and six months ended June 30, 2019, respectively, as compared to €0.7 million and €1.9 million for the three and six months ended June 30, 2018, respectively. The Company’s headcount at June 30, 2019 was approximately 112 full-time equivalents and consisted of 94 employees in the Netherlands and 18 employees in the U.S. A total of 29 employees who are devoted to activities other than R&D and overall management of the Company were included under management and administration costs for the three and six months ended June 30, 2019. The Company’s headcount at June 30, 2018 was approximately 85 full-time equivalents and consisted of 70 employees in the Netherlands and 15 employees in the U.S. A total of 18 employees who were devoted to activities other than R&D and overall management of the Company were included under management and administration costs for the three and six months ended June 30, 2018.

Finance Income (Expense)

Finance Income (Expense)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Finance Income (Expense)	14. Finance Income (Expense) Three months ended Six months ended 2019 2018 2019 2018 (euros in thousands) Finance income Interest income and similar related income 476 494 1,028 834 Net gain on foreign exchange — 6,917 871 4,111 476 7,411 1,899 4,945 Finance costs Interest expense (61 ) (1 ) (96 ) (1 ) Net loss on foreign exchange (1,083 ) — — — (1,144 ) (1 ) (96 ) (1 ) Total finance income (expense) (668 ) 7,410 1,803 4,944 Interest income primarily results from interest earned on cash held on account and accretion of investment earnings. The Company experienced losses on its U.S. dollar denominated cash, cash equivalents and investments of approximately €1.1 million and gains of €0.9 million for the three and six months ended June 30, 2019, respectively, as compared to gains of €6.9 million and €4.1 million for the three and six months ended June 30, 2018. The Company presents foreign currency gains and losses on a net basis as either finance income or finance expense depending on whether foreign currency movements are in a net gain or net loss position. As of June 30, 2019, the Company held approximately $31.1 million and $54.5 million in U.S. dollar denominated cash and cash equivalent accounts and investment accounts, respectively, subject to the fluctuation in foreign currency between the euro and U.S. dollar.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Subsequent Events	15. Subsequent Events The Company has evaluated subsequent events through August 19, 2019, the date of issuance of the unaudited consolidated financial statements for the three and six months ended June 30, 2019. In July 2019, Merus N.V. (the “Company”) entered into a lease (the “Lease”) with Kadans Science Partner XII B.V. (Landlord”), pursuant to which the Company agreed to lease approximately 5,070 square meters of office and laboratory space in a new multi-tenant office building that is to be constructed in Utrecht, the Netherlands (the “Premises”). The initial term of the Lease is ten years from the date that the Premises are completed in accordance with certain specifications provided in a Development Agreement (described below) (the “Completion Date”), which is expected to occur in mid-2022. The Lease will renew for two 5-year terms following the initial term, unless earlier terminated by the Company or the Landlord, except that the earliest the Landlord may terminate the lease is 20 years from the Completion Date. The Lease provides for an estimated initial rent of €1,323,780 per annum and will be due beginning on the Completion Date. The rent amount is subject to adjustment based on the consumer price index (the “CPI”) beginning on January 1, 2019 through the Completion Date an then annually thereafter, subject to certain limitations if the CPI is greater than 3.0%. The final initial rent amount is contingent upon, among other things, the parameters of the final constructed Premises and the CPI adjustment described above, and will be determined upon the Completion Date. The Company is also responsible for certain fit-out costs and service fees related to the Premises. In July 2019, the Company also entered into a Development Agreement with the Landlord and another tenant, Genmab B.V. (the “Development Agreement”), which provides for the design, development and construction of the new multi-tenant office building of which the Premises is a part. Except for the items described above, there were no additional events requiring disclosure in the notes to these financial statements.

Significant accounting polici_2

Significant accounting policies (Policies)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Basis of Presentation	Basis of Presentation These unaudited interim condensed consolidated financial statements (the “interim financial statements”) have been prepared in accordance with International Accounting Standard (“IAS”) 34, Interim Financial Reporting Form 20-F
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with IFRS requires the use of certain critical accounting estimates. It also requires management to exercise its judgment in the process of applying the Company’s accounting policies. The areas involving a higher degree of judgment or complexity or areas where assumptions and estimates are significant to these interim financial statements are disclosed in Note 4. The results of operations for the three and six months ended June 30, 2019 are not necessarily indicative of operations to be expected for the full fiscal year ending December 31, 2019.
Foreign Currency Transactions	Foreign Currency Transactions 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”). The interim financial statements are presented in euros, which is Merus N.V.’s functional currency. The functional currency of Merus US, Inc. is the U.S. dollar. All amounts are rounded to the nearest thousand euros, except where otherwise indicated.
Seasonality	Seasonality The Company’s financial results have varied substantially, and are expected to continue to vary, from period to period. The Company believes that its ordinary activities are not linked to any particular seasonal factors.
Segment Reporting	Segment Reporting The Company operates in one reportable segment, which comprises the discovery and development of innovative bispecific therapeutics.
Cash and Cash Equivalents	Cash and Cash Equivalents For the purpose of presentation in the unaudited condensed consolidated statement of cash flows as well as the unaudited condensed consolidatedstatement of financial position, cash and cash equivalents include deposits held with financial institutions with a maturity of three months or less from the date of acquisition. Cash and cash equivalents include €49.0 million of short-term investments with a three month or less maturity, callable on demand. The carrying values of short-term investments approximate fair value due to their short-term maturities.
Revenue Recognition	Revenue Recognition The Company accounts for revenue in accordance with IFRS 15, Revenue from Contracts with Customers The terms of the contracts within the scope of IFRS 15 may contain multiple promised goods and services, which often include license rights to certain of the Company’s product candidates and research and development (“R&D”) activities. Payments under such agreements include: (i) upfront nonrefundable license fees; (ii) payments for R&D services performed by the Company, including reimbursement for certain external costs; (iii) payments based upon the achievement of certain development, regulatory and commercial milestones; and (iv) royalties on net product sales, if any. Under IFRS 15, the Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the Company expects to receive in exchange for those goods or services. The Company recognizes revenue following the five-step model prescribed under IFRS 15: (i) identification of the contract(s) with the customer; (ii) identification of the performance obligations; (iii) determination of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations in the contract; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. In order to account for contracts with customers, the Company identifies the promised goods or services in the contract and evaluates whether such promised goods or services represent performance obligations. The Company accounts for those components as separate performance obligations when the following criteria are met: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer, and (ii) the Company’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. This evaluation requires subjective determinations and requires the Company to make judgments about the promised goods and services and whether such goods and services are separable from the other aspects of the contractual relationship. In determining the performance obligations, the Company evaluates certain criteria, including whether the promised good or service is capable of being distinct and whether such good or service is distinct within the context of the contract, based on consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research, manufacturing and commercialization capabilities of the customer; the availability of research and manufacturing expertise in the general marketplace; and the level of integration, interrelation, and interdependence among the promises to transfer goods or services. The transaction price is allocated among the performance obligations using the relative selling price method and the applicable revenue recognition criteria are applied to each of the separate performance obligations. At contract inception, the Company determines the standalone selling price for each performance obligation identified in the contract. If an observable price of the promised good or service sold separately is not readily available, the Company utilizes assumptions that require judgment to estimate the standalone selling price, which may include development timelines, probabilities of technical and regulatory success, reimbursement rates for personnel costs, forecasted revenues, potential limitations to the selling price of the product, expected technological life of the product and discount rates. Upfront License Payments If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are not distinct and bundled with other performance obligations, 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 from the combined performance obligation. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestones At the inception of each arrangement that includes pre-commercial milestone cumulative catch-up Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and where 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 royalty revenue. R&D Cost Reimbursement R&D cost reimbursement revenue, which is typically related to reimbursements from customers for the Company’s performance of R&D services under the respective agreements, is recognized on the basis of labor hours valued at a contractually agreed rate. R&D cost reimbursement revenue also includes reimbursements for related out-of-pocket expenses The Company typically acts as the principal under such arrangements and, therefore, records these reimbursements on a gross basis. The impact of the new revenue standard IFRS 15 was also assessed for the instances under the ONO Pharmaceutical Co., Ltd. (“ONO”) research and license agreement where the Company acts as an agent. The Company concluded that no control was obtained for these pass-through arrangements to reimburse costs under the ONO research and license agreement and as such the cost reimbursements were netted in R&D instead of being recognized as revenue. C osts of Obtaining a Contract with a Customer The Company capitalizes the incremental costs of obtaining a contract with a customer if it expects to recover those costs. To date, the Company has not capitalized any incremental costs for obtaining a contract. 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.
Leases	Leases Effective January 1, 2019, the Company adopted IFRS 16, Leases right-of-use IFRS 16 introduces a single lessee accounting model and requires a lessee to recognize assets and liabilities for all leases with a term of more than 12 months, unless the underlying asset is of low value. A lessee is required to recognize a right-of-use Determining whether an Arrangement Contains a Lease At inception of an arrangement, the Company determines whether the arrangement conveys the right to control the use of an identified asset for a period in exchange for consideration, in which case the arrangement is, or contains, a lease. At inception or on reassessment of an arrangement that contains a lease, the Company allocates the consideration in the arrangement to each lease component on the basis of the relative stand-alone price of the lease component and the aggregate stand-alone price of the non-lease non-real non-lease non-lease Lease Assets and Lease Liabilities The Company recognizes a right-of-use The lease liability is initially measured at the present value of outstanding lease payments, discounted using the interest rate implicit in the lease or, if that rate cannot be readily determined, the Company’s incremental borrowing rate. The lease liability is measured at amortized cost using the effective interest method and is remeasured when there is a change in future lease payments arising from a change in an index or rate. A corresponding adjustment is made to the carrying amount of the lease asset. Interest expense related to the Company’s lease liabilities is recognized as a finance expense in the condensed consolidated statement of profit or loss and comprehensive loss. Short-Term Leases and Low Value-Leases The Company has elected not to recognize lease assets and lease liabilities for short-term leases (leases with a term of 12 months or less) and leases of low-value

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Investments	Investments as of June 30, 2019 and December 31, 2018 consisted of the following: Balance as per June 30, December 31, (euros in thousands) Commercial paper 13,929 22,208 U.S. Treasury securities 2,411 6,733 Corporate fixed income bonds 17,465 14,185 Agency bonds 1,755 1,729 Current investments 35,560 44,855 Corporate fixed income bonds 12,319 16,945 Non-current 12,319 16,945 Total investments 47,879 61,800

Trade and Other Receivables (Ta

Trade and Other Receivables (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Trade and Other Receivables Due Within One Year	All receivables as included in the following table are short-term and due within one year. Balance as per June 30, December 31, (euros in thousands) Trade receivables 1,393 2,690 Unbilled receivables 72 236 VAT receivable 684 891 Prepaid expenses 4,526 2,783 Prepaid pension costs 631 — Interest receivable 312 213 Other receivables 677 219 8,295 7,032

Other Liabilities and Accruals

Other Liabilities and Accruals (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Short-term and Payable Within One Year	All amounts are short-term and payable within one year. Balance as per June 30, December 31, (euros in thousands) Audit fees 70 167 Personnel-related 405 560 Accrued bonus 928 1,523 Accrued R&D costs 4,758 4,409 Lease liabilities 1,432 — IP legal fees 258 212 Subsidy advances received 151 42 Other accruals 1,748 1,051 9,750 7,964

Deferred Revenue (Tables)

Deferred Revenue (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Deferred Revenue	Deferred revenue as of June 30, 2019 and December 31, 2018 consisted of the following: Balance as per June 30, December 31, (euros in thousands) Deferred revenue – current portion 17,208 16,934 Deferred revenue 89,666 97,675 106,874 114,609

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Reconciliation of Common Shares Outstanding	The following is a tabular reconciliation of common shares outstanding for the six months ended June 30, 2019 and 2018. Six months ended June 30, 2019 2018 Common Shares outstanding at January 1, 23,358,977 19,429,848 Issued for cash — 3,099,997 Exercise of common share options 9,980 34,041 Vesting of RSUs 24,330 68,914 Common shares outstanding at June 30, 23,393,287 22,632,800
Summary of Inputs Used in the Measurement of the Fair Values and the Related Fair Values at the Grant Dates	The inputs used in the measurement of the fair values and the related fair values at the grant dates for the options granted during the six months ended June 30, 2019 were: Key Management euros ) All Other Personnel euros ) Fair value at grant date 6.07 – 7.60 6.15 – 8.62 Share price at grant date 9.83 – 12.49 9.83 – 14.19 Exercise price 9.83 – 12.49 9.83 – 14.19 Expected volatility (weighted-average) 87.58 % 87.11 % Contractual life 10 years 10 years Expected dividends — % — % Risk-free interest rate (based on government bonds) 2.13%—2.74 % 2.02%—2.65 %
Summary of Reconciliation of Outstanding Share Options	The number of share options and the weighted average exercise prices of share options granted were as follows for the six months ended June 30, 2019: Weighted average euros ) Number of Outstanding at January 1, 2019 14.62 2,633,039 Forfeited during the six months 14.07 (223,631 ) Expired during the six months 15.95 (126,589 ) Exercised during the six months 11.02 (9,980 ) Granted during the six months 10.23 1,009,671 Outstanding at June 30, 2019 13.27 3,282,510 Exercisable at June 30, 2019 13.34 1,533,094
Summary of Number of Share Options Outstanding	The number of options outstanding by group of employees as of June 30, 2019, was as follows: Group of employees entitled June 30, 2019 Key management personnel 2,580,281 All other employees 702,229 Total 3,282,510
Summary of Reconciliation of RSU's	During the six months ended June 30, 2019, the Company did not grant any new RSUs. The following table summarizes the Company’s RSU activity for the six months ended June 30, 2019: Weighted average euros ) Number of Outstanding at January 1, 2019 20.03 101,302 Forfeited during the six months — — Vested during the six months 20.03 (24,330 ) Granted during the six months — — Outstanding at June 30, 2019 — 76,972

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Revenue	The Company’s revenues are generated entirely in the Netherlands. In the following table, revenue is disaggregated by primary source of revenue as follows: Three months ended Six months ended June 30, June 30, June 30, June 30 (euros in thousands) (euros in thousands) Upfront payment amortization 4,231 4,250 8,436 9,087 R&D cost reimbursement 1,383 2,040 3,806 4,556 Milestone revenue 74 139 1,148 2,639 Revenue from contracts with customers 5,688 6,429 13,390 16,282 Income (expense) from grants on research projects (109 ) 114 (109 ) 182 5,579 6,543 13,281 16,464
Summary of Changes in Tarde Receivables, Contract Assets and Contract Liabilities	The following table presents changes in the Company’s trade receivables, contract assets and contract liabilities during the six months ended June 30, 2019: Balance at December 31, Additions Deductions Balance at June 30, (euros in thousands) Trade receivables Trade receivables 2,690 5,819 (7,116 ) 1,393 Total trade receivables 2,690 5,819 (7,116 ) 1,393 Contract assets Unbilled receivables 236 114 (278 ) 72 Total contract assets 236 114 (278 ) 72 Contract liabilities Deferred revenue 114,609 848 (8,583 ) 106,874 Total contract liabilities 114,609 848 (8,583 ) 106,874

Total Operating Expenses (Table

Total Operating Expenses (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Total Operating Expenses	The following table presents a breakdown of operating expenses: Three months ended June 30, Six months ended June 30, 2019 2018 2019 2018 (euros in thousands) Manufacturing costs 450 5,580 2,325 9,858 IP and license costs 585 492 876 844 Personnel related R&D 2,470 2,107 4,510 3,808 Other R&D costs 6,479 4,344 12,644 8,311 Total R&D costs 9,984 12,523 20,355 22,821 Management and administration costs 3,119 2,639 5,055 5,491 Litigation costs 59 552 123 849 Other operating expenses 3,684 2,745 7,624 5,134 Total other expenses 3,743 3,297 7,747 5,983 Total operating expenses 16,846 18,459 33,157 34,295
Breakdown of Other Research and Development Costs	A breakdown of other R&D costs is presented as follows: Three months ended June 30, Six months ended June 30, 2019 2018 2019 2018 ( euros in thousands ) Discovery and preclinical costs 2,055 1,078 4,175 1,763 Clinical costs 3,156 1,850 6,041 4,248 Other R&D costs 1,268 1,416 2,428 2,300 Total other R&D costs 6,479 4,344 12,644 8,311

Employee Benefits (Tables)

Employee Benefits (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Disclosure of Detailed Information About Employee Benefits	Details of the employee benefits are as follows: Three months ended Six months ended 2019 2018 2019 2018 (euros in thousands) Salaries and wages 3,454 2,876 6,476 5,505 WBSO subsidy (1,071 ) (733 ) (2,319 ) (1,900 ) Social security premiums 291 198 579 449 Health insurance 65 69 215 188 Pension costs 294 188 564 390 Share-based compensation 1,806 2,109 3,058 4,554 Other personnel expense 1,150 224 1,786 433 Total employee benefits expense 5,989 4,931 10,359 9,619
Schedule of Share-based Compensation Expenses Recognized as Employee Benefit Expenses	Share-based compensation expense recognized as employee benefit expenses was as follows: Three months ended Six months ended 2019 2018 2019 2018 (euros in thousands) R&D costs 715 714 1,482 1,525 Management and administration costs 919 1,343 1,255 2,852 Other expenses 172 52 321 177 1,806 2,109 3,058 4,554

Finance Income (Expense) (Table

Finance Income (Expense) (Tables)	6 Months Ended
	Jun. 30, 2019
Text block [abstract]
Summary of Finance Income and Expense	Three months ended Six months ended 2019 2018 2019 2018 (euros in thousands) Finance income Interest income and similar related income 476 494 1,028 834 Net gain on foreign exchange — 6,917 871 4,111 476 7,411 1,899 4,945 Finance costs Interest expense (61 ) (1 ) (96 ) (1 ) Net loss on foreign exchange (1,083 ) — — — (1,144 ) (1 ) (96 ) (1 ) Total finance income (expense) (668 ) 7,410 1,803 4,944

General Information - Additiona

General Information - Additional Information (Detail) € / shares in Units, $ / shares in Units, € in Thousands, $ in Millions	Feb. 15, 2018EUR (€)	Feb. 15, 2018USD ($)	Feb. 13, 2018€ / shares$ / sharesshares	Jun. 30, 2019EUR (€)	Jun. 30, 2018EUR (€)	Dec. 31, 2018EUR (€)	Dec. 31, 2017EUR (€)
Disclosure of general information [line items]
Accumulated loss				€ (190,100)
Cash and cash equivalents				131,993	€ 170,327	€ 143,747	€ 149,678
Investments				47,879		€ 61,800
Aggregate purchase price				€ 1	€ 44,731
Investors [member]
Disclosure of general information [line items]
Common shares issued | shares			3,099,997
Issue price per share | € / shares			€ 0.09
Aggregate purchase price	€ 44,800	$ 55.8
Purchase price | $ / shares			€ 18

Significant Accounting Polici_3

Significant Accounting Policies - Additional Information (Detail) € in Millions	6 Months Ended
	Jun. 30, 2019EUR (€)Segment
Disclosure of significant accounting policies [abstract]
Number of reportable segment | Segment	1
Cash and cash equivalents, maximum original maturities	3 months
Short-term investments | €	€ 49

Use of Estimates, Judgments a_2

Use of Estimates, Judgments and Assumptions - Additional Information (Detail) € in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019EUR (€)	Jun. 30, 2018EUR (€)	Jun. 30, 2019EUR (€)	Jun. 30, 2019USD ($)	Jun. 30, 2018EUR (€)
Disclosure of changes in accounting estimates [line items]
Deferred tax assets	€ 0		€ 0
Income tax expense	54	€ 87	120		€ 139
United States [member]
Disclosure of changes in accounting estimates [line items]
Income tax expense	€ 100	€ 100	€ 100		€ 100
Incyte [member] | Dutch [member]
Disclosure of changes in accounting estimates [line items]
Licence fee income | $				$ 120

Investments - Additional Inform

Investments - Additional Information (Detail) - EUR (€) € in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Investment [Line Items]
Non-current investments	€ 12,319		€ 12,319		€ 16,945
Purchases of investments			30,551	€ 29,560
Proceeds from investment maturities			45,114	18,931
Foreign currency exchange gains		€ 6,917	871	€ 4,111
Foreign currency exchange losses	1,083
Mature in 12 months [member]
Investment [Line Items]
Non-current investments	6,500		6,500
Finance Income Expense [Member]
Investment [Line Items]
Foreign currency exchange gains	€ 400
Foreign currency exchange losses			€ 700

Investments - Summary of Invest

Investments - Summary of Investments (Detail) - EUR (€) € in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investment [Line Items]
Investments, current portion	€ 35,560	€ 44,855
Non-current investments	12,319	16,945
Total investments	47,879	61,800
Commercial paper [member]
Investment [Line Items]
Investments, current portion	13,929	22,208
U.S. Treasury securities [member]
Investment [Line Items]
Investments, current portion	2,411	6,733
Corporate fixed income bonds [member]
Investment [Line Items]
Investments, current portion	17,465	14,185
Non-current investments	12,319	16,945
Agency bond [member]
Investment [Line Items]
Investments, current portion	€ 1,755	€ 1,729

Trade and Other Receivables - S

Trade and Other Receivables - Summary of Short-Term Receivables that are Due WIthin One Year (Detail) - EUR (€) € in Thousands	Jun. 30, 2019	Dec. 31, 2018
Trade and other current payables [abstract]
Trade receivables	€ 1,393	€ 2,690
Unbilled receivables	72	236
VAT receivable	684	891
Prepaid expenses	4,526	2,783
Prepaid pension costs	631
Interest receivable	312	213
Other receivables	677	219
Total	€ 8,295	€ 7,032

Trade and Other Receivables - A

Trade and Other Receivables - Additional Information (Detail) - EUR (€) € in Thousands	Jun. 30, 2019	Dec. 31, 2018
Trade and other current payables [abstract]
Taxes and social security liabilities	€ 128	€ 256

Other Liabilities and Accrual_2

Other Liabilities and Accruals - Summary of Short-term and Payable Within One Year (Detail) - EUR (€) € in Thousands	Jun. 30, 2019	Dec. 31, 2018
Disclosure of accruals and other payables [abstract]
Audit fees	€ 70	€ 167
Personnel-related	405	560
Accrued bonus	928	1,523
Accrued R&D costs	4,758	4,409
Lease liabilities	1,432
IP legal fees	258	212
Subsidy advances received	151	42
Other accruals	1,748	1,051
Total	€ 9,750	€ 7,964

Deferred Revenue - Summary of D

Deferred Revenue - Summary of Deferred Revenue (Detail) - EUR (€) € in Thousands	Jun. 30, 2019	Dec. 31, 2018
Disclosure of deferred income [abstract]
Deferred revenue - current portion	€ 17,208	€ 16,934
Deferred revenue	89,666	97,675
Total deferred revenue	€ 106,874	€ 114,609

Deferred Revenue - Additional I

Deferred Revenue - Additional Information (Detail) $ / shares in Units, € in Thousands, $ in Thousands, shares in Millions	Feb. 28, 2017EUR (€)	Feb. 28, 2017USD ($)	Dec. 20, 2016EUR (€)$ / shares	Jan. 31, 2017USD ($)	Jun. 30, 2019EUR (€)shares	Mar. 31, 2019EUR (€)	Mar. 31, 2019USD ($)	Jun. 30, 2019EUR (€)shares	Jun. 30, 2019USD ($)$ / shares	Jun. 30, 2018EUR (€)	Dec. 31, 2018USD ($)	Jun. 30, 2019USD ($)shares	Dec. 31, 2018EUR (€)	Dec. 20, 2016USD ($)
Disclosure of deferred income [line items]
Total deferred revenue					€ 106,874			€ 106,874					€ 114,609
Aggregate purchase price								1		€ 44,731
Revenue recognized					100			200
Upfront and Milestone Payments [member]
Disclosure of deferred income [line items]
Revenue recognized					200			500
Incyte Corporation [member]
Disclosure of deferred income [line items]
Non-refundable upfront payment receivable					€ 112,000			€ 112,000				$ 120,000
Common shares issued | shares					3.2			3.2				3.2
Purchase price per share | $ / shares									$ 25
Aggregate purchase price | $				$ 80,000
Non-refundable upfront payment	€ 112,000	$ 120,000
Incyte collaboration agreement [member]
Disclosure of deferred income [line items]
Total deferred revenue					€ 104,700			€ 104,700					112,600
Non-refundable upfront payment								112,000	$ 120,000
Consideration from the issuance and sale of common shares								143,400	152,600
Simcere collaboration and license agreement [member]
Disclosure of deferred income [line items]
Total deferred revenue					1,600			1,600					€ 2,100
Non-refundable upfront payment								2,300	2,750
Milestone payments								600	800
Betta collaboration and license agreement [member]
Disclosure of deferred income [line items]
Total deferred revenue					€ 600			600
ONO Research and License Agreement [member]
Disclosure of deferred income [line items]
Performance obligation recognized as revenue | $											$ 1,200
Paid for full time equivalent funding								200
Compensate for research service								300
ONO Research and License Agreement [member] | Deferred revenue [member]
Disclosure of deferred income [line items]
Non-refundable upfront payment								700
Incyte share subscription agreement [member]
Disclosure of deferred income [line items]
Total deferred revenue			€ 31,400											$ 32,600
Purchase price per common share | $ / shares			€ 25
Consideration from the issuance and sale of common shares								31,400	32,600
Betta Pharmaceuticals Co Ltd [member]
Disclosure of deferred income [line items]
Non-refundable upfront payment						€ 900	$ 1,000
Milestone payments						€ 10,500	$ 12,000	€ 10,500	$ 12,000

Leases - Additional Information

Leases - Additional Information (Detail) € in Thousands, $ in Millions	Jan. 01, 2019EUR (€)	May 01, 2018	Jun. 30, 2019EUR (€)	Jun. 30, 2019USD ($)
Disclosure of operating lease [abstract]
Operating lease term of lease agreement		5 years	2 years
Leases expiration period			Fourth quarter of 2021
Right-of-use assets	€ 2,800		€ 6,069
Lease liabilities	€ 3,000
Incremental borrowing rate	5.25%		4.50%
Lease agreement term			7 years
Lease assets recognized			€ 3,800	$ 4.3
Lease liabilities			€ 3,800	$ 4.3

Shareholders' Equity - Addition

Shareholders' Equity - Additional Information - Equity (Detail) $ / shares in Units, € in Thousands, $ in Millions	Dec. 21, 2018EUR (€)	Dec. 21, 2018USD ($)	Dec. 20, 2018$ / sharesshares	Feb. 15, 2018EUR (€)	Feb. 15, 2018USD ($)	Feb. 13, 2018$ / sharesshares	Jun. 30, 2019EUR (€)shares	Jun. 30, 2018EUR (€)shares	Dec. 31, 2018EUR (€)	Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)
Disclosure of terms and conditions of share-based payment arrangement [line items]
Aggregate purchase price | €							€ 1	€ 44,731
Investors [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Common shares issued						3,099,997
Aggregate purchase price				€ 44,800	$ 55.8
Purchase price | $ / shares						$ 18
Regeneron Pharmaceuticals, INC [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Common shares issued			600,000
Aggregate purchase price	€ 13,100	$ 15
Purchase price | $ / shares			$ 25
Total proceeds received									€ 13,100	$ 15
Aggregate value of common shares issued									6,000		$ 6.9
Gain on litigation settlement									€ 7,100	$ 8.1
Ordinary shares [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of shares fully issued and paid							23,393,287	22,632,800

Shareholders' Equity - Summary

Shareholders' Equity - Summary of Reconciliation of Common Shares Outstanding (Detail)	6 Months Ended
	Jun. 30, 2019shares	Jun. 30, 2018shares
Disclosure of classes of share capital [line items]
Exercise of common share options	9,980
Vesting of RSUs	24,330
Ordinary shares [member]
Disclosure of classes of share capital [line items]
Common Shares outstanding, Beginning balance	23,358,977	19,429,848
Issued for cash		3,099,997
Exercise of common share options	9,980	34,041
Vesting of RSUs	24,330	68,914
Common shares outstanding, Ending balance	23,393,287	22,632,800

Shareholders' Equity - Additi_2

Shareholders' Equity - Additional Information - Share Based Payment Arrangements (Detail)	6 Months Ended
	Jun. 30, 2019EUR (€)shares	Jun. 30, 2018EUR (€)	Jan. 01, 2019shares	Dec. 31, 2018EUR (€)shares
Disclosure of terms and conditions of share-based payment arrangement [line items]
Share based payment expense	€ 3,100,000	€ 4,600,000
Option granted | shares	1,009,671
Weighted average exercise price	€ 13.27			€ 14.62
Weighted-average remaining contractual life	7 years 3 months 18 days
Weighted-average share price	€ 11.02
Number of share options outstanding in share-based payment arrangement | shares	3,282,510			2,633,039
Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Weighted average exercise price	€ 1.93
Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Weighted average exercise price	€ 27.47
2016 Plan [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Description of options vested	Options granted under the 2016 Plan are exercisable once vested.
Vesting period	4 years
Percentage of initial vesting period	25.00%
Percentage of remaining vesting options	75.00%
Period of remaining option vesting period	36 monthly installments
Percentage of vesting period	100.00%
Description of option lapse	Options will lapse on the tenth anniversary of the date of grant.
Vesting period of Restricted Stock Units vested	4 years
Number of common share entitled to receive | shares	1
Option granted | shares	1,009,671
Option grant fair value	€ 10,300,000
Increase in authorized share | shares			1,469,785	934,359
Non-Executive Compensation Program [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Percentage of initial vesting period	33.00%
Percentage of remaining vesting options	67.00%
Period of remaining option vesting period	24 substantially equal monthly installments
Vesting period	Three-year period
Period of option will be vested and exercised	12 substantially equal monthly installments
Description of grant award	Following the vesting commencement date, such that the subsequent award shall be fully vested on the first anniversary of the date of grant.

Shareholders' Equity - Summar_2

Shareholders' Equity - Summary of Inputs Used in the Measurement of the Fair Values and the Related Fair Values at the Grant Dates (Detail)	6 Months Ended
	Jun. 30, 2019yr€ / shares
Key management personnel [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Expected volatility (weighted-average)	87.58%
Contractual life | yr	10
Expected dividends	0.00%
Key management personnel [member] | Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Fair value at grant date	€ 6.07
Share price at grant date	9.83
Exercise price	€ 9.83
Expected dividends	0.00%
Risk-free interest rate (based on government bonds)	2.13%
Key management personnel [member] | Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Fair value at grant date	€ 7.60
Share price at grant date	12.49
Exercise price	€ 12.49
Expected dividends	0.00%
Risk-free interest rate (based on government bonds)	2.74%
All other employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Expected volatility (weighted-average)	87.11%
Contractual life | yr	10
Expected dividends	0.00%
All other employees [member] | Bottom of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Fair value at grant date	€ 6.15
Share price at grant date	9.83
Exercise price	€ 9.83
Expected dividends	0.00%
Risk-free interest rate (based on government bonds)	2.02%
All other employees [member] | Top of range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Fair value at grant date	€ 8.62
Share price at grant date	14.19
Exercise price	€ 14.19
Expected dividends	0.00%
Risk-free interest rate (based on government bonds)	2.65%

Shareholders' Equity - Summar_3

Shareholders' Equity - Summary of Reconciliation of Outstanding Share Options (Detail)	6 Months Ended
	Jun. 30, 2019EUR (€)shares
Disclosure of terms and conditions of share-based payment arrangement [abstract]
Outstanding at January 1 | shares	2,633,039
Forfeited during the six months | shares	(223,631)
Expired during the six months | shares	(126,589)
Exercised during the six months | shares	(9,980)
Granted during the six months | shares	1,009,671
Outstanding at June 30 | shares	3,282,510
Exercisable at June 30 | shares	1,533,094
Outstanding at January 1 | €	€ 14.62
Forfeited during the six months | €	14.07
Expired during the six months | €	15.95
Exercised during the six months | €	11.02
Granted during the six months | €	10.23
Outstanding at June 30 | €	13.27
Exercisable at June 30 | €	€ 13.34

Shareholders' Equity - Summar_4

Shareholders' Equity - Summary of Number of Share Options Outstanding (Detail) - shares	Jun. 30, 2019	Dec. 31, 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of outstanding share options	3,282,510	2,633,039
Key management personnel [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of outstanding share options	2,580,281
All other employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of outstanding share options	702,229

Shareholders' Equity - Summar_5

Shareholders' Equity - Summary of Reconciliation of RSU's (Detail)	6 Months Ended
	Jun. 30, 2019EUR (€)shares
Disclosure of terms and conditions of share-based payment arrangement [abstract]
Outstanding beginning balance | €	€ 20.03
Forfeited during the six month period | €	0
Vested during the six month period | €	20.03
Granted during the six month period | €	€ 0
Outstanding beginning balance	101,302
Forfeited during the six month period	0
Vested during the six month period	(24,330)
Granted during the six month period	0
Outstanding ending balance	76,972

Revenue - Summary of Revenue (D

Revenue - Summary of Revenue (Detail) - EUR (€) € in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue [line items]
Total Revenue	€ 5,579	€ 6,543	€ 13,281	€ 16,464
Up-front payment amortization [member]
Revenue [line items]
Total Revenue	4,231	4,250	8,436	9,087
R&D cost reimbursement and milestone [member]
Revenue [line items]
Total Revenue	1,383	2,040	3,806	4,556
Milestone Revenue [member]
Revenue [line items]
Total Revenue	74	139	1,148	2,639
Revenue from contracts with customers [member]
Revenue [line items]
Total Revenue	5,688	6,429	13,390	16,282
Income from grants on research projects [member]
Revenue [line items]
Total Revenue	€ (109)	€ 114	€ (109)	€ 182

Revenue - Additional Informatio

Revenue - Additional Information (Detail) - EUR (€) € in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue [line items]
Grant income		€ 0.1		€ 0.2
Reduction in grant income	€ 0.1		€ 0.1
Revenue recognized included in deferred revenue			8.4
Revenue recognized not included in deferred revenue			0.2
Incyte collaboration agreement [member]
Revenue [line items]
Up-front payment amortization	4	4	7.9	7.9
ONO Research and License Agreement [member]
Revenue [line items]
Up-front payment amortization		0.2		1.1
Simcere collaboration and license agreement [member]
Revenue [line items]
Up-front payment amortization	0.1	0.1	0.3	0.1
Betta Pharmaceuticals Co Ltd [member]
Revenue [line items]
Up-front payment amortization	0.1		0.2
ONO Research and License Agreement [member]
Revenue [line items]
Cost reimbursements	0	0.1	0.1	0.2
Milestone revenue	0	0	1	2.5
Payment terms related to receivables					30 days
Simcere Pharmaceutical Co Ltd [member]
Revenue [line items]
Milestone revenue	0.1	0.1	0.1	0.1
Payment terms related to receivables					30 days
Betta Pharmaceuticals Co Ltd [member]
Revenue [line items]
Payment terms related to receivables					60 days
Incyte collaboration agreement [member]
Revenue [line items]
Cost reimbursements	1.4	€ 2	3.6	€ 4.3
Betta Research and License Agreement [member] | Top of range [member]
Revenue [line items]
Cost reimbursements	€ 0.1		€ 0.1

Revenue - Disclosure Of Changes

Revenue - Disclosure Of Changes In Trade Receivables Contract Assets And Contract Liabilities Explanatory (Detail) € in Thousands	6 Months Ended
	Jun. 30, 2019EUR (€)
Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]
Trade receivables, beginning balance	€ 2,690
Trade receivables, additions	5,819
Trade receivables, deductions	(7,116)
Trade receivables, ending balance	1,393
Contract assets, beginning balance	236
Contract assets, additions	114
Contract assets, deductions	(278)
Contract assets, ending balance	72
Contract liabilities, beginning balance	114,609
Contract liabilities, additions	848
Contract liabilities, deductions	(8,583)
Contract liabilities, ending balance	106,874
Deferred revenue [member]
Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]
Contract liabilities, beginning balance	114,609
Contract liabilities, additions	848
Contract liabilities, deductions	(8,583)
Contract liabilities, ending balance	106,874
Trade receivables [member]
Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]
Trade receivables, beginning balance	2,690
Trade receivables, additions	5,819
Trade receivables, deductions	(7,116)
Trade receivables, ending balance	1,393
Unbilled receivables [member]
Disclosure of changes in trade receivables, contract assets and contract liabilities [line items]
Contract assets, beginning balance	236
Contract assets, additions	114
Contract assets, deductions	(278)
Contract assets, ending balance	€ 72

Total Operating Expenses - Summ

Total Operating Expenses - Summary of Total Operating Expenses (Detail) - EUR (€) € in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Operating Expenses [abstract]
Manufacturing costs	€ 450	€ 5,580	€ 2,325	€ 9,858
IP and license costs	585	492	876	844
Personnel related R&D	2,470	2,107	4,510	3,808
Other R&D costs	6,479	4,344	12,644	8,311
Total R&D costs	9,984	12,523	20,355	22,821
Management and administration costs	3,119	2,639	5,055	5,491
Litigation costs	59	552	123	849
Other operating expenses	3,684	2,745	7,624	5,134
Total other expenses	3,743	3,297	7,747	5,983
Total operating expenses	€ 16,846	€ 18,459	€ 33,157	€ 34,295

Total Operating Expenses - Addi

Total Operating Expenses - Additional Information (Detail) - EUR (€) € in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Operating Expenses [abstract]
Research and development costs	€ 9,984	€ 12,523	€ 20,355	€ 22,821
Management and administration costs	3,119	2,639	5,055	5,491
Litigation and opposition	59	552	123	849
Other operating expenses	€ 3,684	€ 2,745	€ 7,624	€ 5,134

Total Operating Expenses - Brea

Total Operating Expenses - Breakdown of Other Research and Development Costs (Detail) - EUR (€) € in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Operating Expenses [abstract]
Discovery and preclinical costs	€ 2,055	€ 1,078	€ 4,175	€ 1,763
Clinical costs	3,156	1,850	6,041	4,248
Other R&D costs	1,268	1,416	2,428	2,300
Total other R&D costs	€ 6,479	€ 4,344	€ 12,644	€ 8,311

Employee Benefits - Disclosure

Employee Benefits - Disclosure of Detailed Information About Employee Benefits (Detail) - EUR (€) € in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Short-term employee benefits expense [abstract]
Salaries and wages	€ 3,454	€ 2,876	€ 6,476	€ 5,505
WBSO subsidy	(1,071)	(733)	(2,319)	(1,900)
Social security premiums	291	198	579	449
Health insurance	65	69	215	188
Pension costs	294	188	564	390
Share-based compensation	1,806	2,109	3,058	4,554
Other personnel expense	1,150	224	1,786	433
Total employee benefits expense	€ 5,989	€ 4,931	€ 10,359	€ 9,619

Employee Benefits - Schedule of

Employee Benefits - Schedule of Share-based Compensation Expenses Recognized as Employee Benefit Expenses (Detail) - EUR (€) € in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Share Of Equity Investment [line items]
Stock award expense	€ 1,806	€ 2,109	€ 3,058	€ 4,554
R&D costs [member]
Disclosure Of Share Of Equity Investment [line items]
Stock award expense	715	714	1,482	1,525
Management and administration costs [member]
Disclosure Of Share Of Equity Investment [line items]
Stock award expense	919	1,343	1,255	2,852
Other expenses [member]
Disclosure Of Share Of Equity Investment [line items]
Stock award expense	€ 172	€ 52	€ 321	€ 177

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail) € in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019EUR (€)Employees	Jun. 30, 2018EUR (€)Employees	Jun. 30, 2019EUR (€)Employees	Jun. 30, 2018EUR (€)Employees
Disclosure of employee benefits [line Items]
Received and recognized subsidies | €	€ 1.1	€ 0.7	€ 2.3	€ 1.9
Number of employees	112	85	112	85
Netherlands [member]
Disclosure of employee benefits [line Items]
Number of employees	94	70	94	70
United States [member]
Disclosure of employee benefits [line Items]
Number of employees	18	15	18	15
Management and administration costs [member]
Disclosure of employee benefits [line Items]
Number of employees	29	18	29	18

Other Income (Expense) - Summar

Other Income (Expense) - Summary of Other Income (Expense) (Detail) - EUR (€) € in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Rental expenses on real estate [abstract]
Interest income and similar related income	€ 476	€ 494	€ 1,028	€ 834
Net gain on foreign exchange		6,917	871	4,111
Finance income	476	7,411	1,899	4,945
Interest expense	(61)	(1)	(96)	(1)
Net loss on foreign exchange	(1,083)
Finance costs	(1,144)	(1)	(96)	(1)
Total finance income (expense)	€ (668)	€ 7,410	€ 1,803	€ 4,944

Finance Income (Expense) - Addi

Finance Income (Expense) - Additional Information (Detail) € in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019EUR (€)	Jun. 30, 2018EUR (€)	Jun. 30, 2019EUR (€)	Jun. 30, 2018EUR (€)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)
Rental expenses on real estate [abstract]
Foreign exchange gain (loss) | €	€ (1.1)	€ 6.9	€ 0.9	€ 4.1
Foreign currency denominated cash and cash equivalent accounts and investment | $					$ 31.1	$ 54.5

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail)	May 01, 2018	Jul. 31, 2019EUR (€)m²	Jun. 30, 2019
Disclosure of Events After Reporting Period [line items]
Operating lease term of lease agreement	5 years		2 years
Non adjusting event [member]
Disclosure of Events After Reporting Period [line items]
Square meter of office space under lease agreement | m²		5,070
Operating lease term of lease agreement		10 years
Leases commencement period		Mid-2022
Operating lease termination period		20 years
Description of additional renewal term		The Lease will renew for two 5-year terms following the initial term
Estimated initial rent per annum | €		€ 1,323,780
Minimum consumer price index (CPI) change for rent amount change		3.00%