uniQure (QURE) 10-K 1 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 25, 2021	Jun. 30, 2020
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-36294
Entity Registrant Name	uniQure N.V.
Entity Incorporation, State or Country Code	P7
Entity Address, Address Line One	Paasheuvelweg 25a
Entity Address, City or Town	1105 BP Amsterdam
Entity Address, Country	NL
City Area Code	31
Local Phone Number	20-240-6000
Title of 12(b) Security	Ordinary shares, par value €0.05 per share
Trading Symbol	QURE
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
ICFR Auditor Attestation Flag	true
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 2,002.7
Entity Common Stock, Shares Outstanding		44,993,987
Entity Central Index Key	0001590560
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 244,932	$ 377,793
Accounts receivables	6,618
Accounts receivable from related party		947
Prepaid expenses	4,337	4,718
Other current assets	3,024	748
Total current assets	258,911	384,206
Non-current assets
Property, plant and equipment, net	32,328	28,771
Operating lease right-of-use assets	26,086	26,797
Intangible assets, net	3,361	5,427
Goodwill	542	496
Restricted cash	2,748	2,933
Deferred tax asset	16,419
Total non-current assets	81,484	64,424
Total assets	340,395	448,630
Current liabilities
Accounts payable	3,772	5,681
Accrued expenses and other current liabilities	18,038	12,457
Current portion of operating lease liabilities	5,524	5,865
Current portion of deferred revenue		7,627
Total current liabilities	27,334	31,630
Non-current liabilities
Long-term debt	35,617	36,062
Operating lease liabilities, net of current portion	30,403	31,133
Deferred revenue, net of current portion		23,138
Derivative financial instruments related party		3,075
Other non-current liabilities	3,136	534
Total non-current liabilities	69,156	93,942
Total liabilities	96,490	125,572
Commitments and contingencies
Shareholders' equity
Ordinary shares, 0.05 par value: 60,000,000 shares authorized at December 31, 2020 and December 31, 2019 and 44,777,799 and 43,711,954 ordinary shares issued and outstanding at December 31, 2020 and December 31, 2019, respectively	2,711	2,651
Additional paid-in-capital	1,016,018	986,803
Accumulated other comprehensive income / (loss)	9,907	(6,689)
Accumulated deficit	(784,731)	(659,707)
Total shareholders' equity	243,905	323,058
Total liabilities and shareholders' equity	$ 340,395	$ 448,630

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) $ in Thousands	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares
CONSOLIDATED BALANCE SHEETS
Accumulated depreciation | $	$ 35,226	$ 28,625
Ordinary shares, authorized	60,000,000	60,000,000
Ordinary shares, issued	44,777,799	43,711,954
Ordinary shares, outstanding	44,777,799	43,711,954

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total revenues	$ 37,514	$ 7,281	$ 11,284
Operating expenses:
Research and development expenses	(122,400)	(94,737)	(74,809)
Selling, general and administrative expenses	(42,580)	(33,544)	(25,305)
Total operating expenses	(164,980)	(128,281)	(100,114)
Other income	3,342	1,888	2,146
Other expense	(1,302)	(2,028)	(1,548)
Loss from operations	(125,426)	(121,140)	(88,232)
Interest income	938	3,547	2,729
Interest expense	(3,825)	(3,810)	(2,160)
Foreign currency (losses) / gains, net	(13,613)	(268)	4,382
Other non-operating gains / (losses), net	483	(2,530)	208
Loss before income tax income / (expense)	(141,443)	(124,201)	(83,073)
Income tax income / (expense)	16,419		(231)
Net loss	(125,024)	(124,201)	(83,304)
Other comprehensive income / (loss):
Foreign currency translation adjustments net of tax impact of nil for the year ended December 31, 2020 (2019: nil and 2018: $(0.2) million)	16,596	570	(5,261)
Total comprehensive loss	$ (108,428)	$ (123,631)	$ (88,565)
Basic and diluted net loss per ordinary share	$ (2,810)	$ (3,110)	$ (2,340)
Weighted average shares used in computing basic and diluted net loss per ordinary share	44,466,365	39,999,450	35,639,745
License revenues
Total revenues	$ 4,352
License revenues from related party
Total revenues	32,967	$ 4,988	$ 7,528
Collaboration revenues
Total revenues	59
Collaboration revenues from related party
Total revenues	$ 136	$ 2,293	$ 3,756

CONSOLIDATED STATEMENTS OF OP_2

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS
Foreign currency translation adjustments, tax	$ 0	$ 0	$ (200,000)

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Ordinary shares	Additional paid-in capital	Accumulated other comprehensive (loss)/incomeCumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated other comprehensive (loss)/income	Accumulated deficitCumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated deficit	Cumulative Effect, Period of Adoption, Adjustment [Member]	Total
Beginning balance at Dec. 31, 2017	$ 1,947	$ 566,530	$ 1,802	$ (3,800)	$ 23,116	$ (475,318)	$ 24,918	$ 89,359
Beginning balance (in shares) at Dec. 31, 2017	31,339,040
Increase (decrease) in shareholders' equity
Loss for the period						(83,304)		(83,304)
Other comprehensive income (loss)				(5,261)				(5,261)
Follow-on public offering	$ 309	138,052						138,361
Follow-on public offering (in shares)	5,175,000
Exercise of share options	$ 19	4,741						4,760
Exercise of share options (in shares)	425,074
Restricted and performance share units distributed during the period	$ 24	(24)
Restricted and performance share units distributed during the period (in shares)	409,948
Share-based compensation expense		10,708						10,708
Issuance of ordinary shares relating to employee stock purchase plan		65						65
Issuance of ordinary shares relating to employee stock purchase plan (in shares)	2,591
Ending balance at Dec. 31, 2018	$ 2,299	720,072		(7,259)		(535,506)		179,606
Ending balance (in shares) at Dec. 31, 2018	37,351,653
Increase (decrease) in shareholders' equity
Loss for the period						(124,201)		(124,201)
Other comprehensive income (loss)				570				570
Follow-on public offering	$ 311	242,363						242,674
Follow-on public offering (in shares)	5,625,000
Hercules warrants exercise	$ 2	1,271						1,273
Hercules warrants exercise (in shares)	37,175
Exercise of share options	$ 25	5,210						5,235
Exercise of share options (in shares)	453,232
Restricted and performance share units distributed during the period	$ 14	(14)
Restricted and performance share units distributed during the period (in shares)	235,692
Share-based compensation expense		17,533						17,533
Issuance of ordinary shares relating to employee stock purchase plan		368						368
Issuance of ordinary shares relating to employee stock purchase plan (in shares)	9,202
Ending balance at Dec. 31, 2019	$ 2,651	986,803		(6,689)		(659,707)		$ 323,058
Ending balance (in shares) at Dec. 31, 2019	43,711,954							43,711,954
Increase (decrease) in shareholders' equity
Accumulated deficit								$ (659,707)
Loss for the period						(125,024)		(125,024)
Other comprehensive income (loss)				16,596				16,596
Exercise of share options	$ 29	7,169						7,198
Exercise of share options (in shares)	498,678
Restricted and performance share units distributed during the period	$ 31	(31)
Restricted and performance share units distributed during the period (in shares)	560,986
Share-based compensation expense		21,831						21,831
Issuance of ordinary shares relating to employee stock purchase plan		246						246
Issuance of ordinary shares relating to employee stock purchase plan (in shares)	6,181
Ending balance at Dec. 31, 2020	$ 2,711	$ 1,016,018		$ 9,907		$ (784,731)		$ 243,905
Ending balance (in shares) at Dec. 31, 2020	44,777,799							44,777,799
Increase (decrease) in shareholders' equity
Accumulated deficit								$ (784,731)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net loss	$ (125,024)	$ (124,201)	$ (83,304)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and impairment losses	10,648	6,669	12,415
Share-based compensation expense	21,831	17,533	10,708
Change in fair value of derivative financial instruments and contingent consideration	(483)	2,530	(4,054)
Unrealized foreign exchange losses / (gains)	14,730	891	(5,502)
Deferred tax (income) / expense	(16,419)		231
Change in lease incentives			(330)
Change in deferred revenue	(33,642)	(4,999)	(8,462)
Changes in operating assets and liabilities:
Accounts receivable and accrued income, prepaid expenses and other current assets	(6,967)	(4,769)	1,578
Accounts payable	(2,701)	1,652	1,065
Accrued expenses, other liabilities and operating leases	3,199	6,010	(382)
Net cash used in operating activities	(134,828)	(98,684)	(76,037)
Cash flows from investing activities
Purchases of intangible assets	(2,213)	(996)	(1,861)
Purchases of property, plant and equipment	(7,271)	(5,651)	(2,384)
Net cash used in investing activities	(9,484)	(6,647)	(4,245)
Cash flows from financing activities
Proceeds from issuance of shares related to employee stock option and purchase plans	7,444	5,603	4,825
Proceeds from public offering of shares, net of issuance costs		242,718	138,361
Proceeds from loan increment			14,775
Proceeds from exercise of warrants		500
Net cash generated from financing activities	7,444	248,821	157,961
Currency effect on cash, cash equivalents and restricted cash	3,822	(106)	(2,187)
Net (decrease) / increase in cash, cash equivalents and restricted cash	(133,046)	143,384	75,491
Cash, cash equivalents and restricted cash at beginning of period	380,726	237,342	161,851
Cash, cash equivalents and restricted cash at the end of period	247,680	380,726	237,342
Total cash, cash equivalents and restricted cash	247,680	237,342	237,342
Supplemental cash flow disclosures:
Cash paid for interest	(4,131)	(3,117)	(2,141)
Non-cash increase / (decrease) in accounts payables and accrued expenses and other current liabilities related to purchases of intangible assets and property, plant, and equipment	$ 630	$ 313	$ (48)

General business information

General business information	12 Months Ended
	Dec. 31, 2020
General business information
General business information	1. General business information ​ uniQure (the “Company”) was incorporated on January 9, 2012 as a private company with limited liability (besloten vennootschap met beperkte aansprakelijkheid) under the laws of the Netherlands. The Company is a leader in the field of gene therapy and seeks to deliver to patients suffering from rare and other devastating diseases single treatments with potentially curative results. The Company’s business was founded in 1998 and was initially operated through its predecessor company, Amsterdam Molecular Therapeutics Holding N.V (“AMT”). In 2012, AMT undertook a corporate reorganization, pursuant to which uniQure B.V. acquired the entire business and assets of AMT and completed a share-for-share exchange with the shareholders of AMT. Effective February 10, 2014, in connection with its initial public offering, the Company converted into a public company with limited liability (naamloze vennootschap) and changed its legal name from uniQure B.V. to uniQure N.V. ​ The Company is registered in the trade register of the Dutch Chamber of Commerce (Kamer van Koophandel) under number 54385229. The Company’s headquarters are in Amsterdam, the Netherlands, and its registered office is located at Paasheuvelweg 25a, Amsterdam 1105 BP, the Netherlands and its telephone number is +31 20 240 6000. The Company’s website address is www.uniqure.com. ​ The Company’s ordinary shares are listed on the Nasdaq Global Select Market and trades under the symbol “QURE”.

Summary of significant accounti

Summary of significant accounting policies	12 Months Ended
	Dec. 31, 2020
Summary of significant accounting policies
Summary of significant accounting policies	2. Summary of significant accounting policies ​ 2.1 Basis of preparation ​ The Company prepared its consolidated financial statements in compliance with generally accepted accounting principles in the United States (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). ​ The consolidated financial statements have been prepared under the historical cost convention, except for derivative financial instruments and contingent consideration, which are recorded at fair value through profit or loss. ​ The consolidated financial statements are presented in U.S. dollars, except where otherwise indicated. Transactions denominated in currencies other than U.S. dollars are presented in the transaction currency with the U.S. dollar amount included in parenthesis, converted at the foreign exchange rate as of the transaction date. ​ The consolidated financial statements presented have been prepared on a going concern basis based on the Company’s cash and cash equivalents as of December 31, 2020 and the Company’s budgeted cash flows for the twelve months following the issuance date. ​ 2.2 ​ The preparation of consolidated financial statements, in conformity with U.S. GAAP and Securities and Exchange Commission (“SEC”) rules and regulations, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the consolidated financial statements and reported amounts of revenues and expenses during the reporting period. Estimates and assumptions are primarily made in relation to the treatment of the commercialization and license agreement entered into between the Company and CSL Behring LLC (“CSL Behring Agreement”), the December 1, 2020, amendment (“amended BMS CLA”) of the 2015 collaboration and license agreement (“BMS CLA”) between the Company and Bristol-Myers Squibb (“BMS”), share-based payments, valuation allowances for deferred tax assets, and accounting for operating leases under ASC 842. If actual results differ from the Company’s estimates, or to the extent these estimates are adjusted in future periods, the Company’s results of operations could either benefit from, or be adversely affected by, any such change in estimate. 2.3 ​ The principal accounting policies applied in the preparation of these consolidated financial statements are set out below. These policies have been consistently applied to all the years presented, unless otherwise stated. ​ 2.3.1 ​ The consolidated financial statements comprise the financial statements of the Company and its subsidiaries. Subsidiaries are all entities over which the Company has a controlling financial interest either through variable interest or through voting interest. Currently, the Company has no involvement with variable interest entities. ​ Inter-company transactions, balances, income, and expenses on transactions between uniQure entities are eliminated in consolidation. Profits and losses resulting from inter-company transactions that are recognized in assets are also eliminated. Accounting policies of subsidiaries have been changed where necessary to ensure consistency with the policies adopted by the Company. ​ 2.3.2 ​ The Company presents assets and liabilities in the consolidated balance sheets based on current and non-current classification. ​ The term current assets is used to designate cash and other assets, or resources commonly identified as those that are reasonably expected to be realized in cash or sold or consumed during the normal operating cycle of the business. The Company’s normal operating cycle is twelve months. All other assets are classified as non-current. ​ The term current liabilities is used principally to designate obligations whose liquidation is reasonably expected to require the use of existing resources properly classifiable as current assets, or the creation of other current liabilities. Current liabilities are expected to be settled in the normal operating cycle. The Company classifies all other liabilities as non-current. ​ Deferred tax assets and liabilities are classified as non-current assets and liabilities, if any. ​ 2.3.3 ​ The functional currency of the Company and each of its entities (except for uniQure Inc.) is the euro (€). This represents the currency of the primary economic environment in which the entities operate. The functional currency of uniQure Inc. is the U.S. dollar ($). The consolidated financial statements are presented in U.S. dollars. ​ Foreign currency transactions are measured and recorded in the functional currency using the exchange rates prevailing at the dates of the transactions. Foreign exchange gains and losses resulting from the settlement of such transactions and from the re-measurement of monetary assets and liabilities denominated in foreign currencies at exchange rates prevailing at balance sheet date are recognized in profit and loss. ​ Upon consolidation, the assets and liabilities of foreign operations are translated into the functional currency of the shareholding entity at the exchange rates prevailing at the balance sheet date; items of income and expense are translated at monthly average exchange rates. The consolidated assets and liabilities are translated from uniQure N.V.’s functional currency, euro, into the reporting currency U.S. dollar at the exchange rates prevailing at the balance sheet date; items of income and expense are translated at monthly average exchange rates. Issued capital and additional paid-in capital are translated at historical rates with differences to the balance sheet date rate recorded as translation adjustments in other comprehensive income / loss. The exchange differences arising on translation for consolidation are recognized in “accumulated other comprehensive income / loss”. On disposal of a foreign operation, the component of other comprehensive income / loss relating to that foreign operation is recognized in profit or loss. ​ 2.3.4 ​ The Company measures certain assets and liabilities at fair value, either upon initial recognition or for subsequent accounting or reporting. ASC 820, Fair Value Measurements and Disclosures ​ ● Level 1 - Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company can access at the measurement date. ​ ● Level 2 - Valuations based on quoted prices for similar assets or liabilities in markets that are not active or models for which the inputs are observable, either directly or indirectly. ​ ● Level 3 - Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and are unobservable. ​ To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. ​ Items measured at fair value on a recurring basis include financial instruments and contingent consideration (Note 4, “Fair value measurement”). The carrying amount of cash and cash equivalents, accounts receivable from collaborators, prepaid expenses, other assets, accounts payable, accrued expenses and other current liabilities reflected in the consolidated balance sheets approximate their fair values due to their short-term maturities. ​ 2.3.5 ​ The consolidated statements of cash flows have been prepared using the indirect method. The cash disclosed in the consolidated statements of cash flows is comprised of cash and cash equivalents. Cash and cash equivalents include bank balances, demand deposits and other short-term highly liquid investments (with maturities of less than three months at the time of purchase) that are readily convertible into a known amount of cash and are subject to an insignificant risk of fluctuation in value. ​ Cash flows denominated in foreign currencies have been translated at the average exchange rates. Exchange differences, if any, affecting cash and cash equivalents are shown separately in the consolidated statements of cash flows. Interest paid and received, and income taxes are included in net cash (used in) provided by operating activities. ​ 2.3.6 ​ Operating segments are identified as a component of an enterprise for which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions on how to allocate resources and assess performance. The Company views its operations and manages its business as one operating segment, which comprises the discovery, development, and commercialization of innovative gene therapies. ​ 2.3.7 ​ The Company follows the provisions of ASC 260, Earnings Per Share ​ Diluted net loss per share reflects the dilution that would occur if share options or warrants to issue ordinary shares were exercised, or performance or restricted share units were distributed. However, potential ordinary shares are excluded if their effect is anti-dilutive. The Company currently has no dilutive securities due to the net loss position and as such, basic and diluted net loss per share are the same for the periods presented. ​ 2.3.8 ​ Long-lived assets, which include property, plant, and equipment and finite-lived intangible assets, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying value of an asset or asset group may not be recoverable. Right-of-use assets are also reviewed for impairment in accordance with ASC 360. The recoverability of the carrying value of an asset or asset group depends on the successful execution of the Company’s business initiatives and its ability to earn sufficient returns on approved products and product candidates. When such events or changes in circumstances occur, the Company assesses recoverability by determining whether the carrying value of such assets will be recovered through the undiscounted expected future cash flows. If the future undiscounted cash flows are less than the carrying amount of these assets, the Company recognizes an impairment loss based on the excess of the carrying value over the fair value of the assets. Fair value is determined through various valuation techniques, including discounted cash flow models, quoted market values, and third-party independent appraisals, as considered necessary. ​ Goodwill is not amortized but is evaluated for impairment within the Company’s single reporting unit on an annual basis, during the fourth quarter, or more frequently if an event occurs or circumstances change that would more-likely-than-not reduce the fair value of the Company’s reporting unit below its carrying amount. The Company performs the same quantitative analysis discussed above for long-lived assets and finite-lived intangible assets. ​ 2.3.9 ​ Property, plant, and equipment is comprised mainly of laboratory equipment, leasehold improvements, construction-in-progress (“CIP”) and office equipment. All property, plant and equipment is stated at cost less accumulated depreciation. CIP consists of capitalized expenses associated with construction of assets not yet placed into service. Depreciation commences on CIP once the asset is placed into service based on its useful life determined at that time. ​ Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss on the transaction is recognized in the consolidated statements of operations and comprehensive loss. ​ Depreciation is calculated using the straight-line method over the estimated useful lives of the assets (or in the case of leasehold improvements a shorter lease term), which are as follows: ​ ​ ​ ​ · Between 10 – 15 years · ​ 5 years · ​ Between 3 – 5 years ​ 2.3.10 ​ The Company adopted ASC 842 using the modified retrospective approach with an effective date as of the beginning of the Company’s fiscal year, January 1, 2019, to operating leases that existed on that date. Comparative financial information related to profit and loss and cash flows for the twelve-month period ended December 31, 2018, was not recast under the new standard, and continues to be presented under ASC 840. ​ The Company measured lease liabilities at the present value of the future lease payments as of January 1, 2019. The Company used an incremental borrowing rate to discount the lease payments. The Company derived the discount rate, adjusted for differences such as in the term and payment patterns, from the Company’s loan from Hercules Technology Growth Capital, Inc (“Hercules Capital”), which was refinanced immediately prior to the January 1, 2019 adoption date in December 2018. The right-of-use asset is valued at the amount of the lease liability reduced by the remaining December 31, 2018 balance of lease incentives received. The lease liability is subsequently measured at the present value of the future lease payments as of the reporting date with a corresponding adjustment to the right-to-use asset. Absent a lease modification, the Company will continue to utilize the January 1, 2019, incremental borrowing rate. ​ ​ The financial results for the years ended December 31, 2020 and 2019 are presented in accordance with ASC 842, while the financial results for the year ended December 31, 2018 are presented in accordance with the Company’s historical accounting policy based on ASC 840. ​ 2.3.11 ​ Deposits paid are either presented as other current assets or as other non-current assets based on duration of the underlying contractual arrangement. Deposits are classified as restricted cash and primarily relate to facility leases. ​ Contract assets are presented in other current assets or as other non-current assets based on the timing of the right to consideration. ​ 2.3.12 ​ Prepaid expenses are amounts paid in the period, for which the benefit has not been realized, and include payments made for insurance and research and clinical contracts. The related expense will be recognized in the subsequent period as incurred. ​ 2.3.13 ​ ​ 2.3.14 ​ Accounts payables are invoiced amounts related to obligations to pay for goods or services that have been acquired in the ordinary course of business from suppliers. Accounts payables are recognized at the amounts invoiced by suppliers. ​ Accrued expenses are recognized for goods or services that have been acquired in the ordinary course of business. ​ Contract liabilities are presented in accounts payable and accrued expenses. ​ 2.3.15 ​ Long-term debt is initially recognized at cost and presented net of original issue discount or premium and debt issuance costs on the consolidated balance sheets. Amortization of debt discount and debt issuance costs is recognized as interest expense in profit and loss over the period of the debt, using the effective interest rate method. ​ 2.3.16 Pensions and other post-retirement benefit plans ​ The Company has a defined contribution pension plan for all employees at its Amsterdam facility in the Netherlands, which is funded by the Company through payments to an insurance company, with individual accounts for each participants’ assets. The Company has no legal or constructive obligation to pay further contributions if the plan does not hold sufficient assets to pay all employees the benefits relating to services rendered in the current and prior periods. The contributions are expensed as incurred. Prepaid contributions are recognized as an asset to the extent that a cash refund or a reduction in the future payments is available. ​ Starting in 2016, the Company adopted a qualified 401(k) Plan for all employees at its Lexington facility in the USA, which offers both a pre-tax and post-tax (Roth) component. Employees may contribute up to 50% of their pre-tax compensation, which is subject to IRS statutory limits for each calendar year. The Company matches $0.50 for every $1.00 contributed to the plan by participants up to 6% of base compensation. Employer contributions are recognized as they are contributed, as long as the employee is rendering services in that period. If employer contributions are made in periods after an individual retires or terminates, the estimated cost is accrued during the employee’s service period. ​ 2.3.17 ​ The Company accounts for its share-based compensation awards in accordance with ASC 718, Compensation-Stock Compensation. ​ All the Company’s share-based compensation plans for employees are equity-classified. ​ ASC 718 requires all share-based compensation to employees, including grants of employee options, restricted share units, performance share units and modifications to existing instruments, to be recognized in the consolidated statements of operations and comprehensive loss based on their grant-date fair values, net of an estimated forfeiture rate, over the requisite service period. Forfeitures of employee options are recognized as they occur. The requirements of ASC 718 are also applied to nonemployee share-based payment transactions except for specific guidance on certain inputs to an option-pricing model and the attribution of cost. ​ The Company uses a Hull & White option model to determine the fair value of option awards. The model captures early exercises by assuming that the likelihood of exercises will increase when the share-price reaches defined multiples of the strike price. This analysis is performed over the full contractual term. ​ 2.3.18 Revenue recognition ​ The Company primarily generates revenue from its collaboration, research, and license agreements with its collaboration partner BMS for the development and commercialization of product candidates. The Company initially entered into these agreements in 2015 and amended them in 2020. ​ On January 1, 2018, the Company adopted new revenue recognition policies in accordance with ASC 606 using the modified retrospective approach. The Company evaluated the initial BMS CLA and determined that its performance obligations were as follows: ​ ● Providing pre-clinical research activities (“Collaboration Revenue”); ● Providing clinical and commercial manufacturing services for products (“Manufacturing Revenue”); and ● Providing access to its technology and know-how in the field of gene therapy as well as actively contributing to the target selection, the collaboration as a whole, the development during the target selection, the pre-clinical and the clinical phase through participating in joint steering committee and other governing bodies (“License Revenue”). As further discussed in Note 3, “Collaboration arrangements and concentration of credit risk”, as a result of the December 2020 amended BMS CLA, the Company’s performance obligation related to License Revenues was materially completed as of the date of the amendment effective date of December 1, 2020. The Company may still be required to provide pre-clinical research activities or clinical and commercial manufacturing services when BMS exercises its options for those services. ​ License Revenue ​ Until the December 2020 amendment of the BMS CLA the Company recognized License Revenue over the expected performance period based on its measure of progress towards the completion of certain activities related to its services. Following the December 2020 amendment of the BMS CLA the Company’s performance was materially completed and it had satisfied its performance obligation (see Note 3, “Collaboration arrangements and concentration of credit risk”, for a detailed discussion). ​ Collaboration and Manufacturing Revenue ​ The Company recognizes Collaboration Revenues associated to optional work orders it receives from BMS to provide analytical development and process development activities that are reimbursable by BMS in accordance with the BMS CLA as well as the amended BMS CLA. ​ BMS and the Company entered into a Master Clinical Supply Agreement in April 2017 for the Company to supply gene therapy products during the clinical phase as well as into a binding term sheet to supply gene therapy products during the commercial phase to BMS. In December 2020, BMS and the Company also entered into a Research Supply Agreement. Revenues from product sales will be recognized when earned. The Company will provide these services as it receives optional work orders from BMS in relation to such services. ​ 2.3.19 ​ The Company receives certain government and regional grants, which support its research efforts in defined projects, and include contributions towards the cost of research and development. These grants generally provide for reimbursement of approved costs incurred as defined in the respective grants and are deferred and recognized in the statements of operations and comprehensive loss over the period necessary to match them with the costs they are intended to compensate, when it is probable that the Company has complied with any conditions attached to the grant and will receive the reimbursement. ​ The Company’s other income also consists of income from the subleasing of the Amsterdam facility while other expense consists of expenses incurred in relation to the subleasing income. ​ 2.3.20 ​ Research and development costs are expensed as incurred. Research and development expenses generally consist of laboratory research, clinical trials, statistical analysis, and report writing, regulatory compliance costs incurred with clinical research organizations and other third-party vendors (including post-approval commitments to conduct consistency and comparability studies). In addition, research and development expenses consist of start-up and validation costs related to the Company’s Lexington facility and the development and improvement of the Company’s manufacturing processes and methods. Furthermore, research and development costs include costs of materials and costs of intangible assets purchased from others for use in research and development activities. The costs of intangibles that are purchased from others for a particular research and development project and that have no alternative future uses (in other research and development projects or otherwise) are expensed as research and development costs at the time the costs are incurred or at the time when no alternative future use is identified. ​ 2.3.21 ​ Income taxes are recorded in accordance with ASC 740, Income Taxes ​ The benefits of tax positions are recognized only if those positions are more likely than not, based on the technical merits, to be sustained upon examination. Recognized tax positions are measured at the largest amount of tax benefit that is greater than 50 percent likely of being realized upon settlement. The determination as to whether the tax benefit will more-likely-than-not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2020, and 2019, the Company did not have any significant unrecognized tax benefits. ​ 2.3.22 Recently Adopted Accounting Pronouncements ​ ASU 2018-13: Fair Value Measurement ​ In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820) which modifies the disclosure requirements on fair value measurements. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019, which for the Company was January 1, 2020. The new disclosure requirements for changes in unrealized gains and losses in other comprehensive income for recurring Level 3 measurements, the range and weighted average of significant unobservable inputs and the amended requirements for the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively. ASU 2018-13 did not have a material impact on the Company’s consolidated financial statements. ​ Recent Accounting Pronouncements Not Yet Effective ​ None. ​

Collaboration arrangements and

Collaboration arrangements and concentration of credit risk	12 Months Ended
	Dec. 31, 2020
Collaboration arrangements and concentration of credit risk
Collaboration arrangements and concentration of credit risk	3. Collaboration arrangements and concentration of credit risk ​ CSL Behring collaboration ​ On June 24, 2020, uniQure biopharma B.V., a wholly-owned subsidiary of uniQure N.V., entered into the CSL Behring Agreement with CSL Behring LLC, (“CSL Behring”), pursuant to which CSL Behring will receive exclusive global rights to etranacogene dezaparvovec, the Company’s investigational gene therapy for patients with hemophilia B, (the “Product”). ​ Under the terms of the CSL Behring Agreement, the Company will receive a $450.0 million upfront cash payment upon the closing of the CSL Behring Agreement and be eligible to receive up to $1.6 billion in additional payments based on regulatory and commercial milestones. The CSL Behring Agreement also provides that the Company will be eligible to receive tiered double-digit royalties in a range of up to a low-twenties percent of net sales of the Product based on sales thresholds. Pursuant to the CSL Behring Agreement, the Company will be responsible for the completion of the HOPE-B clinical trial, manufacturing process validation, and the manufacturing supply of the Product until such time that these capabilities may be transferred to CSL Behring or its designated contract manufacturing organization. Concurrently with the execution of the CSL Behring Agreement, the Company and CSL Behring entered into a development and commercial supply agreement, pursuant to which, among other things, the Company will supply the Product to CSL Behring at an agreed-upon price. Clinical development and regulatory activities performed by the Company pursuant to the CSL Behring Agreement will be reimbursed by CSL Behring. CSL Behring will be responsible for global regulatory submissions and commercialization requirements for the Product. The effectiveness of the transactions contemplated by the CSL Behring Agreement is contingent on completion of review under antitrust laws in the United States, Australia, and the United Kingdom, and certain provisions of the CSL Behring Agreement will not become effective until after we receive all such regulatory approvals. As of December 31, 2020, such regulatory approvals had not been received in all jurisdictions. As of December 31, 2020, the Company concluded it has no enforceable right to the upfront payment, the regulatory and sale milestone payments, or the royalties (together “CSL Behring License Revenue”) that the Company may receive in accordance with the CSL Behring Agreement, as all payments are contingent upon the successful completion of reviews under the Hart-Scott-Rodino Antitrust Improvements Act of 1976. Therefore, the Company determined it will not recognize any revenue in relation to the CSL Behring License Revenue, in accordance with ASC 606 during the year ended December 31, 2020. In accordance with its existing license and other agreements, the Company is contractually required to pay in total a low to high single digit percentage of any upfront payment to its licensors and financial advisor (“License Fees”). The Company did not not The Company incurred $2.1 million of expenses related to the obligations related to the CSL Behring Agreement that had not been satisfied as of December 31, 2020. The Company capitalized these expenses as contract fulfillment costs (presented within Other current assets). As of December 31, 2020, the Company also recognized a $2.1 million receivable (presented within Accounts receivable) from CSL Behring for expenses for which it has a right of reimbursement as well as a contract liability (presented within Accrued expenses and other current liabilities) for the same amount. In accordance with ASC 606 it cannot recognize any CSL Behring License Revenue as of this date. Bristol-Myers Squibb collaboration ​ 2015 Agreement ​ In May 2015, the Company entered into the BMS CLA and various related agreements with BMS, which the Company collectively refers to as the BMS CLA, which provided BMS with exclusive access to the Company’s gene therapy technology platform for the research, development and commercialization of therapeutics aimed at multiple Collaboration Targets. The initial four-year research term under the collaboration terminated on May 21, 2019. During the initial research term of the BMS CLA, the Company supported BMS in discovery, non-clinical, analytical and process development efforts in respect of the Collaboration Targets. For any Collaboration Targets that may be advanced, the Company will be responsible for manufacturing of clinical and commercial supplies. BMS reimbursed the Company for all its research and development costs in support of the collaboration, and will lead development, regulatory and commercial activities for any Collaboration Targets that may be advanced. The BMS CLA initially provided that the Company and BMS could potentially have collaborated on up to ten Collaboration Targets in total. ​ BMS initially designated four Collaboration Targets, including S100A1 for congestive heart failure (“AMT-126”). In October 2018, the Company and BMS completed a heart function proof-of-concept study of AMT-126 in a pre-clinical, diseased animal model. The data did not show a benefit on heart function at six months and, consequently, work on S100A1 was discontinued. The Company impaired a $5.4 million acquired research and development asset associated with the program and released a contingent liability of $3.8 million related to the acquisition of the asset to income in the year ended December 31, 2018. In April 2019, BMS designated a new cardiovascular Collaboration Target to replace S100A1. As a result, BMS had designated a total of four Collaboration Targets as of December 31, 2019. ​ 2020 Amendment ​ In February 2019, BMS requested a one-year extension of the initial research term. In April 2019, following an assessment of the progress of the collaboration and the Company’s expanding proprietary programs, the Company notified BMS that the Company did not intend to agree to an extension of the initial research term but rather preferred to restructure or amend the collaboration to reduce or eliminate certain of the Company’s obligations under it. ​ On December 1, 2020, the Company and BMS entered into the amended BMS CLA. Under the amended BMS CLA, BMS is limited to four Collaboration Targets. For a period of one-year from the effective date of the amended BMS CLA, BMS may replace up to two of these four Collaboration Targets with up to two new targets in the field of cardiovascular disease. The Company continues to be eligible to receive research, development, and regulatory milestone payments of up to $217.0 million for each Collaboration Target, if defined milestones are achieved. ​ BMS is no longer entitled to designate the fifth to tenth Collaboration Targets and as such the Company’s remaining obligations under the amended BMS CLA are substantially reduced. The Company is no longer entitled to receive up to an aggregate $16.5 million in target designation payments for the research, development and regulatory milestone payments associated with the fifth to tenth Collaboration Targets. ​ For as long as any of the four Collaboration Targets are being advanced, BMS may place a purchase order to be supplied with research, clinical and commercial supplies. Subject to the terms of the amended BMS CLA, BMS has the right to terminate the research, clinical and commercial supply relationships, and has certain remedies for failures of supply, up to and including technology transfer for any such failure that otherwise cannot be reasonably resolved. Both BMS and the Company may agree to a technology transfer of manufacturing capabilities pursuant to the terms of the amended BMS CLA. ​ The amended BMS CLA does not extend the initial research term. BMS may place purchase orders to provide limited services primarily related to analytical and development efforts in respect of the four Collaboration Targets. BMS may request such services for a period not to exceed the earlier of (i) the completion of all activities under a Research Plan and (ii) either (A) three years after the last replacement target has been designated by BMS during the one year replacement period following the amended BMS CLA effective date or (B) three years if no replacement targets are designated during this one year period and BMS continues to reimburse the Company for these services. ​ The Company evaluated the impact of the amendment of the BMS CLA in relation to its performance obligation related to: ​ – The Company did not identify any new distinct performance obligations and determined the amended BMS CLA did not represent a separate contract in accordance with ASC 606. The Company evaluated the effect the modification has on its measure of progress towards the completion of its performance obligation related to License Revenue and recorded an adjustment to License Revenue as of December 1, 2020. ​ Services to BMS are rendered by the Dutch operating entity. Total collaboration and license revenue generated with BMS are as follows (presented as revenue from a related party until November 30, 2020, and as revenue from December 1, 2020 onwards): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 ​ ​ 2019 ​ ​ 2018 ​ ​ (in thousands) Bristol Myers Squibb $ 37,514 ​ $ 7,281 ​ $ 11,284 Total $ 37,514 ​ $ 7,281 ​ $ 11,284 ​ Amounts owed by BMS in relation to the Collaboration and License Revenue are as follows (presented as “Accounts receivables” as of December 31, 2020 and as “Accounts receivable from related party” as of December 31, 2019): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Bristol Myers Squibb ​ $ 4,536 ​ $ 947 Total ​ $ 4,536 ​ $ 947 ​ Collaboration Revenue ​ The Company recognizes collaboration revenues associated with Collaboration Target-specific pre-clinical analytical development and process development activities that are reimbursable by BMS under the BMS CLA and the amended BMS CLA as well as other related agreements. Collaboration Revenue related to these contracted services is recognized when performance obligations are satisfied. ​ The Company generated $0.2 million collaboration revenue for the year ended December 31, 2020 (December 31, 2019: $2.3 million; December 31, 2018: $3.8 million). License Revenue ​ The Company recognized $33.0 million of License Revenue for the year ended December 31, 2020 (December 31, 2019: $5.0 million, December 31, 2018: $7.5 million). On May 21, 2015, the Company recorded a $60.1 million upfront payment and in August 2015 it recorded a $15.0 million payment it received from BMS in relation to the designation of the second, third and fourth Collaboration Targets. The Company recognizes License Revenue over the expected performance period based on its measure of progress towards the completion of certain activities related to its services. The Company determines such progress by comparing activities performed at the end of each reporting period with total activities expected to be performed. The Company estimates total expected activities using several unobservable inputs, such as the probability of BMS designating additional targets, the probability of successfully completing each phase and estimated time required to provide services during the various development stages. The estimation of total services at the end of each reporting period involves considerable judgement. The amount of services the Company expects to provide is significantly impacted by the number of Collaboration Targets that it estimates BMS would pursue. As a result of the December 1, 2020 amendment of the BMS CLA the Company no longer is required to potentially provide any services in relation to six additional targets that BMS might have designated. The Company determined its remaining performance obligation is immaterial. The Company adjusted its measure of progress towards the completion of its activities related to its services as of the December 1, 2020 modification date accordingly. The Company recognized the remaining balance of unrecognized License Revenue as of November 30, 2020 of $27.8 million in profit and loss during the year ended December 31, 2020 as License Revenue from a related party. The Company includes variable consideration related to any research, development, and regulatory milestone payments, in the transaction price once it is considered probable that including these payments in the transaction price would not result in the reversal of cumulative revenue recognized. Due to the significant uncertainty surrounding the development of gene-therapy product candidates and the dependence on BMS’s performance and decisions, the Company does not currently (with below exception) consider this probable. ​ On December 17, 2020 BMS designated one of the four Collaboration Targets as a candidate to advance into IND-enabling studies entitling the Company to receive a $4.4 million research milestone payment. The Company recorded the $4.4 million as License Revenue in the twelve-month period ended December 31, 2020. The Company recognizes License Revenue related to product sales by BMS from any of the Collaboration Targets when the sales occur. The Company is eligible to receive net sales-based milestone payments and tiered mid-single to low double-digit royalties on product sales. The royalty term is determined on a licensed-product-by-licensed-product and country-by-country basis and begins on the first commercial sale of a licensed product in a country and ends on the expiration of the last to expire of specified patents or regulatory exclusivity covering such licensed product in such country or, with a customary royalty reduction, ten years after the first commercial sale if there is no such exclusivity. ​

Fair value measurement

Fair value measurement	12 Months Ended
	Dec. 31, 2020
Fair value measurement
Fair value measurement	4. Fair value measurement ​ The Company measures certain financial assets and liabilities at fair value, either upon initial recognition or for subsequent accounting or reporting. ​ The carrying amount of cash and cash equivalents, accounts receivable from collaborators, prepaid expenses, other assets, accounts payable, accrued expenses and other current liabilities reflected in the consolidated balance sheets approximate their fair values due to their short-term maturities. ​ The Company’s only material financial assets measured at fair value using Level 1 inputs is cash and cash equivalents. ​ The liability measured at fair value using Level 3 inputs as of December 31, 2020 was the derivative financial instrument. The Company had recorded derivative financial instruments as of December 31, 2019, that were measured at fair value using Level 3 inputs. Changes in Level 3 items during the years ended December 31, 2020, 2019 and 2018 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivative ​ ​ ​ ​ ​ Contingent ​ financial ​ ​ ​ ​ consideration instruments Total ​ ​ (in thousands) Balance at December 31, 2017 ​ $ 3,964 ​ $ 1,635 ​ $ 5,599 Net gains recognized in profit or loss ​ ​ (3,846) ​ ​ (208) ​ ​ (4,054) Currency translation effects ​ ​ (118) ​ ​ (52) ​ ​ (170) Balance at December 31, 2018 ​ $ — ​ $ 1,375 ​ $ 1,375 Net losses recognized in profit or loss ​ ​ — ​ ​ 2,530 ​ ​ 2,530 Exercise of Hercules warrants ​ ​ — ​ ​ (770) ​ ​ (770) Currency translation effects ​ ​ — ​ ​ (60) ​ ​ (60) Balance at December 31, 2019 ​ $ — ​ $ 3,075 ​ $ 3,075 Net gains recognized in profit or loss ​ ​ — ​ ​ (2,300) ​ ​ (2,300) Derecognition of warrants ​ ​ — ​ ​ (796) ​ ​ (796) Recognition of derivative financial liability of CoC-payment ​ ​ — ​ ​ 2,613 ​ ​ 2,613 Currency translation effects ​ ​ — ​ ​ 53 ​ ​ 53 Balance at December 31, 2020 ​ $ — ​ $ 2,645 ​ $ 2,645 ​ Derivative financial instruments ​ The Company issued derivative financial instruments related to its collaboration with BMS and in relation to the issuance of the Hercules loan facility. ​ Derivative financial instruments BMS ​ Pursuant to the BMS CLA, the Company in 2015 granted BMS two warrants that were subsequently terminated in connection with the amendment to the BMS CLA on December 1, 2020. The Company granted to BMS: ​ ● A warrant that allowed BMS to purchase a specific number of the Company’s ordinary shares such that its ownership would have equaled 14.9% immediately after such purchase (“1 st warrant”). The 1 st warrant could have been exercised on the later of (i) the date on which the Company received from BMS the Target Designation Fees (as defined in the BMS CLA) associated with the first six new targets (a total of seven Collaboration Targets); and (ii) the date on which BMS designated the sixth new target (the seventh Collaboration Target); and ● A warrant that allowed BMS to purchase a specific number of the Company’s ordinary shares such that its ownership would have equaled 19.9% immediately after such purchase (“2 nd warrant” and together with 1 st warrant, the “warrants”). The warrant could have been exercised on the later of (i) the date on which the Company received from BMS the Target Designation Fees associated with the first nine new targets (a total of ten Collaboration Targets); and (ii) the date on which BMS designated the ninth new target (the tenth Collaboration Target). On December 1, 2020, the Company derecognized the warrants when these were terminated in accordance with the amended BMS CLA. ​ Pursuant to the terms of the BMS CLA the exercise price in respect of each warrant was equal to the greater of (i) the product of (A) $33.84 , multiplied by (B) a compounded annual growth rate of 10% (or approximately $57.32 as of November 30, 2020) and (ii) the product of (A) 1.10 multiplied by (B) the weighted average volume price (“VWAP”) for the 20 trading days ending on the date that is five trading days prior to the date of a notice of exercise delivered by BMS. ​ The fair value of the warrants as of December 31, 2019 was $3.1 million. During the year ended December 31, 2020, the Company recognized a $3.1 million gain in non-operating income / expense (December 31, 2019: $2.3 million loss; December 31, 2018: $0.5 million gain) related to fair value changes of the BMS warrants. The gain recognized in the year ended December 31, 2020 includes $0.8 million from the derecognition of the BMS warrants on December 1, 2020. ​ The Company used Monte-Carlo simulations to determine the fair market value of the BMS warrants. The valuation model incorporated several inputs, the risk-free rate adjusted for the period affected, an expected volatility based on historical Company volatility, the expected yield on any dividends and management’s expectations on the timelines of reaching certain defined trigger events for the exercising of the warrants, as well as management’s expectations regarding the number of ordinary shares that would be issued upon exercise of the warrants. All of these represent Level 3 inputs. Additionally, the model assumed BMS would exercise the warrants only if it was financially rational to do so. ​ The warrants could only have been exercised following the occurrence of events contractually defined in the warrant agreements. The probability of the occurrence of these events represented another significant unobservable input used in the calculation of the fair value of the warrants. ​ On December 1, 2020, the Company and BMS terminated the BMS warrants and agreed that upon the consummation of a change of control transaction of uniQure that occurs prior to December 1, 2026 or BMS’ delivery of a target cessation notice for all four Collaboration Targets, uniQure (or its third party acquirer) shall pay to BMS a one-time, non-refundable, non-creditable cash payment of $70.0 million, provided that (x) if $70.0 million is greater than five percent (5.0%) of the net proceeds (as contractually defined) from such change of control transaction, the payment shall be an amount equal to five percent of such net proceeds, and (y) if $70.0 million is less than one percent of such net proceeds, the change of control payment shall be an amount equal to one percent of such net proceeds (“CoC-payment”). The Company has not consummated any change of control transaction as of December 31, 2020 that would obligate it to make a CoC-payment. The Company determined that the CoC-payment should be recorded as a derivative financial liability as of December 1, 2020 and that subsequent changes in the fair market value of this derivative financial liability should be recorded in profit and loss. The fair market value of the derivative financial liability is materially impacted by probability that market participants assign to the likelihood of the occurrence of a change of control transaction that would give rise to a CoC-payment. This probability represents an unobservable input. The Company determined the fair market value of the derivative financial liability by using a present value model based on expected cash flow. The expected cash flows are materially impacted by the probability that market participants assign to the likelihood of the occurrence of a change of control event within the biotechnology industry. The Company estimated this unobservable input using the best information available as of December 1, 2020 and December 31, 2020. The Company obtained reasonably available market information that it believed market participants would use in determining the likelihood of the occurrence of a change-of control transaction within the biotechnology industry. Selecting and evaluating market information involves considerable judgement and uncertainty. Based on all such information and its judgment the Company estimated that the fair market value of the derivative financial liability (presented within “Other non-current liabilities”) as of December 1, 2020 and December 31, 2020 was $2.6 million. The Company recorded a $2.6 million loss within “Other non-operating expenses” in the twelve-month period ended December 31, 2020 related to the initial recognition of this derivative financial liability. ​ Hercules loan facility ​ On June 14, 2013, the Company entered into a venture debt loan facility (the “Original Facility”) with Hercules (see Note 8, “Long-term debt”) pursuant to a Loan and Security Agreement (the “Loan Agreement”), which included a warrant maturing on February 5, 2019. The warrant was not closely related to the host contract and was accounted for separately as a derivative financial liability measured at fair value though profit or loss. The warrant included in the Original Facility remained in place following the 2014, 2016 and 2018 amendments of the loan. The Hercules warrants were exercised as of February 1, 2019. The Company issued 37,175 ordinary shares at $34.25 following the exercise of all Hercules warrants and receipt of $0.5 million from Hercules. During the year ended December 31, 2020, the Company recognized no more gains or losses in other non-operating income / (expense) (December 31, 2019: $0.2 million loss; December 31, 2018: $0.3 million loss) related to fair value changes of the Hercules warrants. ​ Contingent consideration ​ In connection with the Company’s acquisition of the InoCard business (“InoCard”) in 2014, the Company recorded contingent consideration related to amounts potentially payable to InoCard’s former shareholders. The amounts payable in accordance with the sale and purchase agreement (as amended in August 2017) were contingent upon realization of milestones associated with its S100A1 protein research program. Following the discontinuation of the research program the Company since 2018 no longer expects to realize those milestones and recorded a $3.8 million gain within research and development expenses for the year ended December 31, 2018, to release the liability to profit and loss.

Property, plant and equipment,

Property, plant and equipment, net	12 Months Ended
	Dec. 31, 2020
Property, plant and equipment, net
Property, plant and equipment, net	5. Property, plant, and equipment, net ​ The following table presents the Company’s property, plant, and equipment as of December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Leasehold improvements ​ $ 37,849 ​ $ 34,611 Laboratory equipment ​ ​ 22,106 ​ ​ 18,232 Office equipment ​ ​ 5,025 ​ ​ 4,212 Construction-in-progress ​ ​ 2,574 ​ ​ 341 Total property, plant, and equipment ​ ​ 67,554 ​ ​ 57,396 Less accumulated depreciation ​ ​ (35,226) ​ ​ (28,625) Property, plant and equipment, net ​ $ 32,328 ​ $ 28,771 ​ Total depreciation expense was $5.7 million for the year ended December 31, 2020 (December 31, 2019: $6.0 million, December 31, 2018: $6.5 million). Depreciation expense is allocated to research and development expenses to the extent it relates to the Company’s manufacturing facility and equipment and laboratory equipment. All other depreciation expenses are allocated to selling, general and administrative expense. ​ The following table summarizes property, plant, and equipment by geographic region. ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Lexington, Massachusetts (United States of America) ​ $ 15,949 ​ $ 15,490 Amsterdam (the Netherlands) ​ 16,379 ​ 13,281 Total ​ $ 32,328 ​ $ 28,771 ​

Right-of-use asset and lease li

Right-of-use asset and lease liabilities	12 Months Ended
	Dec. 31, 2020
Right-of-use asset and lease liabilities
Right-of-use asset and lease liabilities	6. Right-of-use asset and lease liabilities ​ The Company adopted ASU 2016-02 “Leases (Topic 842)” as well as ASU 2018-10 and ASU 2018-11, which both relate to improvements to ASC 842. The Company adopted the standard using the modified retrospective approach with an effective date as of the beginning of the Company’s fiscal year, January 1, 2019 (“new lease accounting standard”). The standard requires the balance sheet recognition for leases. Prior years were not recast under the new standard and therefore, those amounts are presented in accordance with the requirements of the previously effective lease standard ASC 840 (“historic lease accounting standard”). The Company elected to utilize practical expedients available for expired or existing contracts which allowed the Company to carryforward historical assessments of (1) whether contracts are or contain leases, (2) lease classification, and (3) initial direct costs. ​ The Company’s most significant leases relate to office and laboratory space under the following operating lease agreements: ​ Lexington, Massachusetts / United States ​ In July 2013, the Company entered into a lease for a facility in Lexington, Massachusetts, United States. The term of the lease commenced in November 2013, was set for 10 years starting from the 2014 rent commencement date and is non-cancellable. Originally, the lease for this facility had a termination date of 2024. In November 2018, the term was expanded by five years to June 2029. The lease continues to be renewable for two subsequent five-year terms. Additionally, the lease was expanded to include an additional 30,655 square feet within the same facility and for the same term. The lease of the expansion space commenced on June 1, 2019. ​ The contractually fixed annual increase of lease payments through 2029 for both the extension and expansion lease have been included in the lease payments. ​ Amsterdam / The Netherlands ​ In March 2016, the Company entered into a 16-year lease for a facility in Amsterdam, the Netherlands and amended this agreement in June 2016. The Company consolidated its three Amsterdam sites into the new site at the end of May 2017. The lease for the new facility terminates in 2032, with an option to extend in increments of five-year periods. The lease contract includes variable lease payments related to annual increases in payments based on a consumer price index. ​ On December 1, 2017, the Company entered into an agreement to sub-lease three of the seven floors of its Amsterdam facility for a ten-year term ending on December 31, 2027, with an option for the sub-lessee to extend until December 31, 2031. In February 2020, the Company amended the agreement to sub-lease to take back one of the three floors effective March 1, 2020. The fixed lease payments to be received during the remaining term under the agreement to sub-lease amount to $6.6 million (EUR 5.4 million) as of December 31, 2020. ​ Operating lease liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2020 2019 ​ ​ (in thousands) Operating lease cost ​ $ 5,052 ​ $ 4,474 Variable lease cost ​ ​ 607 ​ ​ 507 Sublease income ​ ​ (904) ​ ​ (1,053) Total lease cost ​ $ 4,755 ​ $ 3,928 ​ The rent expense in accordance with the historical lease accounting standard for the year ended December 31, 2018, was calculated on a straight-line basis over the term of the lease and considered $12.2 million of lease incentives received. Aggregate rent expense was as follows: ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2018 ​ ​ (in thousands) Rent expense - Lexington ​ $ 1,583 Rent expense - Amsterdam ​ ​ 1,667 Total lease cost ​ $ 3,250 ​ The table below presents the lease-related assets and liabilities recorded on the Consolidate balance sheets in accordance with the new lease accounting standard. ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Assets ​ ​ ​ ​ ​ ​ Operating lease right-of-use assets ​ $ 26,086 ​ ​ 26,797 Liabilities ​ ​ ​ ​ ​ ​ Current ​ ​ ​ ​ ​ ​ Current operating lease liabilities ​ ​ 5,524 ​ ​ 5,865 Non-current ​ ​ ​ ​ ​ ​ Non-current operating lease liabilities ​ ​ 30,403 ​ ​ 31,133 Total lease liabilities ​ $ 35,927 ​ ​ 36,998 ​ Other information The weighted-average remaining lease term as of December 31, 2020, is 9.4 years, compared to 10.3 years as of December 31, 2019, and the weighted-average discount rate as of December 31, 2020, is 11.37% , compared to 11.33% as of December 31, 2019. The Company derived the weighted-average discount rate, adjusted for differences such as in the term and payment patterns, from the Company’s loan from Hercules capital which was refinanced immediately prior to the January 1, 2019, adoption date in December 2018. The table below presents supplemental cash flow and non-cash information related to leases required in accordance with the new lease accounting standard. ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2020 2019 ​ ​ (in thousands) Operating cash flows for operating leases (1) ​ $ 5,769 ​ $ 4,717 ​ (1) The Company has received $1.5 million of landlord incentive payments for the year ended December 31, 2019, which are not included in the cash paid amounts.) The Company did not obtain any right-of-use assets in exchange for the lease obligations during the year ended December 31, 2020. Besides the initial recognition of operating right-of-use assets of $19.0 million upon adoption of the new lease standards on January 1, 2019, the Company obtained $9.0 million of additional right-of-use assets in exchange for lease obligations during the year ended December 31, 2019. ​ ​ ​ ​ ​ ​ ​ ​ Undiscounted cash flows The table below reconciles the undiscounted cash flows as of December 31, 2020, for each of the first five years and the total of the remaining years to the operating lease liabilities recorded on the Consolidated balance sheet as of December 31, 2020 in accordance with the new lease accounting standard. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Lexington ​ Amsterdam (1) ​ Total ​ (in thousands) 2021 $ 3,455 ​ $ 2,069 ​ $ 5,524 2022 ​ 3,552 ​ ​ 2,069 ​ ​ 5,621 2023 ​ 3,650 ​ ​ 2,069 ​ ​ 5,719 2024 ​ 4,146 ​ ​ 2,069 ​ ​ 6,215 2025 ​ 4,465 ​ ​ 2,069 ​ ​ 6,534 Thereafter ​ 16,279 ​ ​ 12,239 ​ ​ 28,518 Total lease payments $ 35,547 ​ $ 22,584 ​ $ 58,131 ​ ​ ​ ​ ​ ​ ​ ​ ​ Less: amount of lease payments representing interest payments ​ (12,576) ​ ​ (9,628) ​ ​ (22,204) Present value of lease payments ​ 22,971 ​ ​ 12,956 ​ ​ 35,927 Less: current operating lease liabilities ​ (3,455) ​ ​ (2,069) ​ ​ (5,524) Non-current operating lease liabilities $ 19,516 ​ $ 10,887 ​ $ 30,403 (1) Payments are due in EUR and have been translated at the foreign exchange rate as of December 31, 2020, of $1.23 / €1.00)

Intangible assets

Intangible assets	12 Months Ended
	Dec. 31, 2020
Intangible assets
Intangible assets	​ 7. Intangible assets ​ a. Acquired licenses ​ The following table presents the Company’s acquired licenses as of December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Licenses ​ $ 5,660 ​ $ 8,317 Less accumulated amortization and impairment ​ ​ (2,299) ​ ​ (2,890) Licenses, net ​ $ 3,361 ​ $ 5,427 ​ All intangible assets are owned by uniQure biopharma B.V, a subsidiary of the Company. The acquired licenses have a weighted average remaining life of 8.5 years as of December 31, 2020. ​ During the year ended December 31, 2020, the Company capitalized $2.2 million of expenditures related to costs incurred in relation to rights to exclusively evaluate certain technologies during a two-year period that commenced on February 1, 2020. During the same period, the Company disposed of a number of licenses determined to have no alternative future use. During the year ended December 31, 2019, the Company capitalized $1.0 million of expenditures related to ​ As of December 31, 2020, the estimated future amortization expense for each of the five succeeding years and the period thereafter is as follows: ​ ​ ​ ​ ​ Years Amount ​ ​ (in thousands) 2021 ​ $ 1,277 2022 ​ 427 2023 ​ 144 2024 ​ 144 2025 ​ 144 Thereafter ​ 1,225 Total ​ $ 3,361 ​ The amortization expense related to licenses for the year ended December 31, 2020 was $4.6 million (December 31, 2019: $0.6 million; December 31, 2018: $0.4 million). The impairment expense related to licenses for the year ended December 31, 2020 was $0.3 million (December 31, 2019: $0.0 million; December 31, 2018 $0.1 million). ​ b. ​ The Company acquired research and development assets as part of its acquisition of InoCard in July 2014. Based on the review of pre-clinical data associated with those assets, the Company does not expect that it will pursue further research related to those assets. Accordingly, the Company recorded a $5.4 million impairment loss within research and development expenses in the year ended December 31, 2018, to reduce the asset’s carrying amount to its fair value of nil.

Accrued expenses and other curr

Accrued expenses and other current liabilities	12 Months Ended
	Dec. 31, 2020
Accrued expenses and other current liabilities
Accrued expenses and other current liabilities	8. Accrued expenses and other current liabilities ​ Accrued expenses and other current liabilities include the following items: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Accruals for services provided by vendors-not yet billed ​ $ 8,269 ​ $ 5,425 Personnel related accruals and liabilities ​ ​ 7,687 ​ ​ 7,032 Contract liability (see Note 3. Collaboration arrangements) ​ ​ 2,082 ​ ​ — Total ​ $ 18,038 ​ $ 12,457 ​ ​

Long-term debt

Long-term debt	12 Months Ended
	Dec. 31, 2020
Long-term debt
Long-term debt	9. Long-term debt ​ On June 14, 2013, the Company entered into a venture debt loan facility with Hercules, which was amended and restated on June 26, 2014, and again on May 6, 2016 (“2016 Amended Facility”). On December 6, 2018, the Company signed an amendment to the Second Amended and Restated Loan and Security Agreement that both refinanced the then-existing $20.0 million 2016 Amended Facility and provided an additional unconditional commitment of $15.0 million as well as a conditional commitment of $15.0 million that expired on June 30, 2020 (the “2018 Amended Facility”). At signing of the 2018 Amended Facility, the Company drew down an additional $15.0 million for a total of $35.0 million outstanding. The 2018 Amended Facility extended the loan’s maturity date from May 1, 2020 until June 1, 2023. The interest-only period was initially extended from November 2018 to January 1, 2021, and was further extended to January 1, 2022, as a result of meeting the provision in the 2018 Amended Facility of raising more than $90.0 million in equity financing in September 2019. The Company is required to repay the facility in equal monthly installments of principal and interest between the end of the interest-only period and the maturity date. The interest rate continues to be adjustable and is the greater of (i) 8.85% or (ii) 8.85% plus the prime rate less 5.50% per annum. ​ Under the 2018 Amended Facility, the Company paid a facility fee of 0.50% of the $35.0 million outstanding as of signing and owes a back-end fee of 4.95% of the outstanding debt. In addition, in May 2020 the Company paid a back-end fee of $1.0 million in relation to the 2016 Amended Facility. ​ The amortized cost (including interest due presented as part of accrued expenses and other current liabilities) of the 2018 Amended Facility was $35.9 million as of December 31, 2020, compared to $36.3 million as of December 31, 2019, and is recorded net of discount and debt issuance costs. The foreign currency gain on the loan was $3.1 million in 2020 (2019: loss of $0.7 million; 2018: loss of $0.9 million). The fair value of the loan approximates its carrying amount. Inputs to the fair value of the loan are considered Level 3 inputs. ​ Interest expense recorded during the years ended December 31 was as follows: ​ ​ ​ ​ ​ Years Amount ​ ​ (in millions) 2020 ​ $ 3.7 2019 ​ 3.7 2018 ​ ​ 2.0 ​ As a covenant in the 2018 Amended Facility, the Company has periodic reporting requirements and is required to keep a minimum cash balance deposited in bank accounts in the United States, equivalent to the lesser of (i) 65% of the outstanding balance of principal due or (ii) 100% of worldwide cash and cash equivalents. This restriction on cash and cash equivalents only relates to the location of the cash and cash equivalents, and such cash and cash equivalents can be used at the discretion of the Company. In combination with other covenants, the 2018 Amended Facility restricts the Company’s ability to, among other things, incur future indebtedness and obtain additional debt financing, to make investments in securities or in other companies, to transfer assets, to perform certain corporate changes, to make loans to employees, officers, and directors, and to make dividend payments and other distributions. The Company secured the facilities by directly or indirectly pledging its total assets of $340.4 million with the exception of $115.2 million of cash and cash equivalents and other current assets held by uniQure N.V. ​ The 2018 Amended Facility contains provisions that include the occurrence of a material adverse effect, as defined therein, which would entitle Hercules to declare all principal, interest and other amounts owed by the Company immediately due and payable. As of December 31, 2020, the Company was in compliance with all covenants and provisions. ​ The aggregate maturities of the loan, including $7.4 million of coupon interest payments and financing fees, for each of the 29 months after December 31, 2020, are as follows (prior to the January 2021 loan amendment – see Note 18, “Subsequent events”): ​ ​ ​ ​ ​ Years Amount ​ ​ (in thousands) 2021 ​ $ 3,141 2022 ​ 25,002 2023 ​ ​ 14,269 Total ​ $ 42,412 ​

Shareholders' equity

Shareholders' equity	12 Months Ended
	Dec. 31, 2020
Shareholders' equity
Shareholders' equity	10. Shareholders’ equity ​ As of December 31, 2020, the Company’s authorized share capital is €3.0 million (or $3.7 million when translated at an exchange rate as of December 31, 2020, of $1.23 / €1.00), divided into 60,000,000 ordinary shares, each with a nominal value of €0.05. Under Dutch law, the authorized share capital is the maximum capital that the Company may issue without amending its articles of association. ​ All ordinary shares issued by the Company were fully paid. Besides the minimum amount of share capital to be held under Dutch law, there are no distribution restrictions applicable to the equity of the Company. ​ As of December 31, 2020, and 2019 and 2018 the Company’s reserves were restricted for payment of dividends for an accumulated foreign currency translation gain of $9.9 million in 2020 and accumulated foreign currency translation losses of $6.7 million and $7.3 million in 2019 and 2018, respectively. ​ ​ On May 7, 2018, the Company completed a follow-on public offering of 5,175,000 ordinary shares at a public offering price of $28.50 per ordinary share, resulting in gross proceeds to the Company of $147.5 million. The net proceeds to the Company from this offering were $138.4 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. The Company deducted $0.2 million of expenses incurred related to this offering from additional paid-in capital in the accompanying consolidated balance sheet and reflected this within the proceeds from public offering of shares, net of issuance costs within the cash flows from financing activities. ​ In February 2019, the Company issued 37,175 ordinary shares to Hercules pursuant to exercised warrants for $0.5 million in aggregate cash consideration. The Company deemed the sale and issuance of these shares to be exempt from registration under the Securities Act in reliance on Regulation S of the Securities Act, as an offshore offering of securities and such shares were issued as restricted shares. Hercules represented to us that they were in compliance with the requirements of Regulation S. ​ ​ ​ ​ ​

Share-based compensation

Share-based compensation	12 Months Ended
	Dec. 31, 2020
Share-based compensation
Share-based compensation	11. Share-based compensation ​ Share-based compensation expense recognized by classification included in the consolidated statements of operations and comprehensive loss was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Research and development ​ $ 11,965 ​ $ 8,029 ​ $ 3,994 Selling, general and administrative ​ ​ 9,823 ​ ​ 9,439 ​ ​ 6,699 Total ​ $ 21,788 ​ $ 17,468 ​ $ 10,693 ​ Share-based compensation expense recognized by award type was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Award type ​ ​ ​ ​ ​ ​ ​ ​ ​ Share options ​ $ 11,434 ​ $ 7,896 ​ $ 4,766 Restricted share units ​ ​ 7,364 ​ ​ 4,117 ​ ​ 3,020 Performance share units ​ ​ 2,990 ​ ​ 5,455 ​ ​ 2,907 Total ​ $ 21,788 ​ $ 17,468 ​ $ 10,693 ​ ​ As of December 31, 2020, the unrecognized compensation cost related to unvested awards under the various share-based compensation plans were: ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized Weighted average ​ share-based remaining ​ ​ compensation ​ period for ​ ​ expense ​ recognition ​ ​ (in thousands) ​ (in years) Award type ​ ​ ​ ​ ​ Share options ​ $ 23,492 ​ 2.78 Restricted share units ​ ​ 14,489 ​ 2.09 Performance share units ​ ​ 1,763 ​ 1.03 Total ​ $ 39,744 ​ 2.45 ​ The Company satisfies the exercise of share options and vesting of Restricted Share Units (“RSUs”) and Performance Share Units (“PSUs”) through newly issued shares. ​ The Company’s share-based compensation plans include the 2014 Amended and Restated Share Option Plan (the “2014 Plan”) and inducement grants under Rule 5653(c)(4) of The Nasdaq Global Select Market with terms similar to the 2014 Plan (together the “2014 Plans”). The Company previously had a 2012 Equity Incentive Plan (the “2012 Plan”). As of December 31, 2020, 14,000 fully vested share options are outstanding (December 31, 2019: 14,000) under the 2012 Plan. ​ At the general meeting of shareholders on January 9, 2014, the Company’s shareholders approved the adoption of the 2014 Plan. At the annual general meetings of shareholders in June 2015, 2016 and 2018, uniQure shareholders approved amendments of the 2014 Plan, increasing the shares authorized for issuance by 1,070,000 shares in 2015, 3,000,000 in 2016 and 3,000,000 shares in 2018, for a total of 8,601,471 shares. Share options Share options are priced on the date of grant and, except for certain grants made to non-executive directors, vest over a period of four years . The first 25% vests after one year from the initial grant date and the remainder vests in equal quarterly installments over years two, three and four. Certain grants to non-executive directors vest in full after one year . Any options that vest must be exercised by the tenth anniversary of the initial grant date. 2014 Plan The following tables summarize option activity under the Company’s 2014 Plans for the year ended December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options ​ ​ Number of ​ Weighted average ​ Weighted average ​ Aggregate intrinsic ​ ordinary shares exercise price remaining contractual life value ​ ​ ​ ​ ​ ​ ​ in years ​ ​ (in thousands) Outstanding at December 31, 2019 ​ 2,683,104 ​ $ 21.29 ​ 7.46 ​ $ 135,238 Granted ​ 653,852 ​ $ 49.63 ​ ​ ​ ​ ​ Forfeited ​ (172,548) ​ $ 42.03 ​ ​ ​ ​ ​ Expired ​ (6,451) ​ $ 45.76 ​ ​ ​ ​ ​ Exercised ​ (498,678) ​ $ 14.43 ​ ​ ​ ​ ​ Outstanding at December 31, 2020 ​ 2,659,279 ​ $ 28.13 ​ 7.18 ​ ​ 32,729 Thereof, fully vested and exercisable at December 31, 2020 ​ 1,542,405 ​ $ 18.05 ​ 6.15 ​ ​ 29,161 Thereof, outstanding and expected to vest after December 31, 2020 ​ 1,116,874 ​ $ 42.06 ​ 8.61 ​ ​ 3,568 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding and expected to vest at December 31, 2019 ​ 1,346,337 ​ $ 28.76 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total weighted average grant date fair value of options issued during the period (in $ millions) ​ ​ ​ $ 18.4 ​ ​ ​ ​ ​ Granted to directors and officers during the period (options, grant date fair value $ in millions) ​ 209,254 ​ $ 5.7 ​ ​ ​ ​ ​ Proceeds from option sales during the period (in $ millions) ​ ​ ​ $ 7.2 ​ ​ ​ ​ ​ ​ The following table summarizes information about the weighted average grant-date fair value of options during the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average ​ ​ Options ​ grant ‑ date fair value Granted, 2020 653,852 ​ $ 28.08 Granted, 2019 647,526 ​ ​ 23.57 Granted, 2018 937,832 ​ ​ 15.90 Vested, 2020 ​ 713,924 ​ ​ 14.04 Forfeited, 2020 ​ (172,548) ​ ​ 24.63 ​ The following table summarizes information about the weighted average grant-date fair value of options at December 31: ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average ​ ​ Options ​ grant ‑ date fair value Outstanding and expected to vest, 2020 1,116,874 ​ $ 24.25 Outstanding and expected to vest, 2019 1,346,337 ​ ​ 17.05 ​ The fair value of each option issued is estimated at the respective grant date using the Hull & White option pricing model with the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, Assumptions 2020 2019 ​ 2018 Expected volatility ​ 70% ​ 70% - 75% ​ 75% - 80% Expected terms ​ 10 years ​ 10 years ​ 10 years Risk free interest rate ​ 0.76% - 1.44% ​ 1.92% - 2.87% ​ 2.67% - 3.20% Expected dividend yield ​ 0% ​ 0% ​ 0% ​ The Hull & White option model captures early exercises by assuming that the likelihood of exercises will increase when the share price reaches defined multiples of the strike price. This analysis is performed over the full contractual term. ​ The following table summarizes information about options exercised during the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ Exercised ​ ​ ​ ​ during the year ​ Intrinsic value ​ ​ ​ ​ (in thousands) 2020 498,678 ​ $ 11,927 2019 434,665 ​ 17,700 2018 388,203 ​ 7,515 ​ Restricted Share Units ​ The following table summarizes the RSU activity for the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ RSU ​ ​ Weighted average ​ ​ Number of ​ grant-date fair ​ ​ ordinary shares ​ value Non-vested at December 31, 2019 ​ 370,830 ​ $ 28.62 Granted ​ 376,799 ​ $ 48.18 Vested ​ (206,881) ​ $ 24.18 Forfeited ​ (73,404) ​ $ 46.41 Non-vested at December 31, 2020 ​ 467,344 ​ $ 43.56 ​ ​ ​ ​ ​ ​ Total weighted average grant date fair value of RSUs granted during the period (in $ millions) ​ ​ ​ $ 18.2 Granted to directors and officers during the period (shares, $ in millions) ​ 158,623 ​ $ 7.4 ​ The following table summarizes information about the weighted average grant-date fair value of RSUs granted during the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ Granted Weighted average ​ ​ during the year ​ grant ‑ date fair value 2020 376,799 ​ $ 48.18 2019 198,504 ​ ​ 38.63 2018 262,599 ​ ​ 23.61 ​ The following table summarizes information about the total fair value of RSUs that vested during the years ended December 31: ​ ​ ​ ​ ​ Total fair value ​ (in thousands) 2020 $ 12,156 2019 10,152 2018 8,546 ​ RSUs generally vest over one to three years . RSUs granted to non-executive directors will vest one year from the date of grant. ​ Performance Share Units ​ The following table summarizes the PSU activity for the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ PSU ​ ​ Weighted average ​ ​ Number of ​ grant-date fair ​ ​ ordinary shares ​ value Non-vested at December 31, 2019 ​ 479,422 ​ $ 21.17 Granted ​ 91,003 ​ $ 57.56 Vested ​ (354,105) ​ $ 17.44 Forfeited ​ (3,706) ​ $ 57.56 Non-vested at December 31, 2020 ​ 212,614 ​ $ 42.32 ​ ​ ​ ​ ​ ​ Total weighted average grant date fair value of PSUs granted during the period (in $ millions) ​ ​ ​ $ 5.2 ​ In January 2019, the Company awarded PSUs to its executives and other members of senior management. These PSUs were earned in January 2020 based on the Board’s assessment of the level of achievement of agreed upon performance targets through December 31, 2019. The PSUs awarded for the year ended December 31, 2019 will vest on the third anniversary of the grant, subject to the grantee’s continued employment. ​ The following table summarizes information about the weighted average grant-date fair value, determined at of the date these were earned, of PSUs granted during the years ended December 31: ​ ​ ​ ​ ​ ​ ​ ​ Granted Weighted average ​ ​ during the year ​ grant ‑ date fair value 2020 91,003 ​ $ 57.56 2019 132,362 ​ $ 31.71 2018 — ​ $ — ​ The following table summarizes information about the total fair value of PSUs that vested during the years ended December 31: ​ ​ ​ ​ ​ Total fair value ​ (in thousands) 2020 $ 21,852 2019 1,056 2018 1,350 ​ Employee Share Purchase Plan (“ESPP”) ​ In June 2018, the Company’s shareholders adopted and approved an ESPP allowing the Company to issue up to 150,000 ordinary shares. The ESPP is intended to qualify under Section 423 of the Internal Revenue Code of 1986. Under the ESPP, employees are eligible to purchase ordinary shares through payroll deductions, subject to any plan limitations. The purchase price of the shares on each purchase date is equal to 85% of the lower of the closing market price on the offering date or the closing market price on the purchase date of each three-month offering period. During the year ended December 31, 2020, 6,181 shares have been issued (December 31, 2019: 9,202 and December 31, 2018: 2,591). As of December 31, 2020, a total of 132,026 ordinary shares remains available for issuance under the ESPP plan.

Expenses by nature

Expenses by nature	12 Months Ended
	Dec. 31, 2020
Expenses by nature
Expenses by nature	12. Expenses by nature ​ Operating expenses excluding expenses presented in other expenses included the following expenses by nature: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) Employee-related expenses ​ $ 75,926 ​ $ 59,130 ​ $ 46,254 Laboratory and development expenses ​ 35,977 ​ 30,130 ​ 23,596 Office and housing expenses ​ 13,388 ​ 10,588 ​ 7,281 Legal and advisory expenses ​ 17,370 ​ 11,297 ​ 7,748 Depreciation, amortization, and impairment expenses ​ 10,648 ​ 6,669 ​ 12,415 Patent and license expenses ​ 2,899 ​ 1,654 ​ 1,202 Other operating expenses ​ 8,772 ​ 8,813 ​ 1,618 Total ​ $ 164,980 ​ $ 128,281 ​ $ 100,114 ​ Details of employee-related expenses for the years ended December 31 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) Wages and salaries ​ $ 40,919 ​ $ 32,029 ​ $ 26,646 Share-based compensation expenses ​ 21,831 ​ 17,533 ​ 10,708 Consultant expenses ​ 2,423 ​ 2,464 ​ 2,974 Social security costs ​ 4,068 ​ 2,727 ​ 2,231 Health insurance ​ 2,271 ​ 1,933 ​ 1,471 Pension costs - defined contribution plans ​ 1,779 ​ 1,052 ​ 907 Other employee expenses ​ 2,635 ​ 1,392 ​ 1,317 Total ​ $ 75,926 ​ $ 59,130 ​ $ 46,254 ​

Other non-operating income _ (e

Other non-operating income / (expense)	12 Months Ended
	Dec. 31, 2020
Other non-operating income / (expense)
Other non-operating income / (expense)	13. Other non-operating income / (expense) ​ Other non-operating income / (expense) consists of changes in the fair value of derivative financial instruments (see Note 4, “Fair value measurement”). ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Other non-operating income: ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivative gains ​ $ 483 ​ $ — ​ $ 208 Total other non-operating income: ​ ​ 483 ​ ​ — ​ ​ 208 Other non-operating expense: ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivative losses ​ ​ — ​ ​ (2,530) ​ ​ — Total other non-operating expense: ​ ​ — ​ ​ (2,530) ​ ​ — Other non-operating income / (expense), net ​ $ 483 ​ $ (2,530) ​ $ 208 ​ The Company recorded a net gain of $0.5 million for the year ended December 31, 2020, compared to a net loss of $2.3 million and a net gain of $0.5 million for the years ended December 31, 2019 and December 31, 2018, respectively, related to the derivative financial instruments issued as part of its collaboration with BMS. The $0.5 million gain for the year ended December 31, 2020 includes a $2.3 million gain related to the reduction of the fair market value of the BMS warrants, a $0.8 million gain related to the derecognition of the BMS warrants on December 1, 2020 and a $2.6 million loss related to the initial recognition of the derivative financial liability related to the CoC-payment. The Company recorded a net loss of $0.2 million and $0.3 million for the years ended December 31, 2019 and December 31, 2018, respectively, related to warrants issued to Hercules. ​ ​

Income taxes

Income taxes	12 Months Ended
	Dec. 31, 2020
Income taxes
Income taxes	14. Income taxes ​ a. Income tax benefit / (expense) ​ No current ​ There are no significant unrecognized tax benefits as of December 31, 2020 and 2019. ​ For the years ended December 31, 2020, 2019 and 2018, loss before income taxes consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) Dutch operations ​ $ (130,493) ​ $ (111,820) ​ $ (85,721) U.S. operations ​ (10,950) ​ (12,381) ​ 2,646 Foreign operations ​ — ​ — ​ 3 Total ​ $ (141,443) ​ $ (124,201) ​ $ (83,073) ​ The income tax benefit / (expense) for the years ended December 31, 2020, 2019 and 2018, consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) Current tax expense ​ ​ ​ ​ ​ ​ ​ ​ ​ Dutch operations ​ $ — ​ $ — ​ $ — U.S. operations ​ — ​ — ​ — Foreign operations ​ — ​ ​ — ​ (22) Total current tax expense ​ $ — ​ $ — ​ $ (22) Deferred tax benefit / (expense) ​ ​ ​ ​ ​ ​ Dutch operations ​ $ — ​ $ — ​ $ (209) U.S. operations ​ 16,419 ​ — ​ — Foreign operations ​ — ​ — ​ — Total deferred tax benefit / (expense) ​ $ 16,419 ​ $ — ​ $ (209) Total income tax benefit / (expense) ​ $ 16,419 ​ $ — ​ $ (231) ​ b. Tax rate reconciliation ​ The reconciliation of the amount of income tax benefit / (expense) that would result from applying the Dutch statutory income tax rate to the Company’s reported amount of income tax benefit / (expense) for the years ended December 31, 2020, 2019 and 2018, is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Loss before income tax income / (expense) for the period ​ $ (141,443) ​ $ (124,201) ​ $ (83,073) Expected income tax benefit at the tax rate enacted in the Netherlands (25%) ​ 35,361 ​ 31,050 ​ 20,768 Difference in tax rates between the Netherlands and the U.S. as well as other foreign countries ​ 247 ​ (495) ​ (106) Release of valuation allowance related to expected future taxable income of U.S. operations ​ ​ 16,419 ​ ​ — ​ ​ — Other net change in valuation allowance ​ (30,568) ​ (25,583) ​ (19,207) Nondeductible expenses ​ (5,041) ​ (4,972) ​ (2,648) Change in fair value of contingent consideration ​ — ​ — ​ 962 Income tax benefit / (expense) ​ $ 16,419 ​ $ — ​ $ (231) ​ Nondeductible expenses predominantly relate to share-based compensation expenses and affected the effective tax rate by an amount of $5.8 million in 2020 (2019: $4.4 million; 2018: $2.7 million). Derivative financial instruments affected the effective tax rate by income of $0.8 million in 2020 (expense of $0.6 million in 2019; $0.0 million in 2018), which reduced the nondeductible expenses resulting from share-based compensation expenses. ​ c. ​ The tax effects of temporary differences and carryforwards that give rise to significant portions of deferred tax assets and deferred tax liabilities at December 31, 2020 and 2019 are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Deferred tax assets: ​ ​ Net operating loss carryforwards ​ $ 158,614 ​ $ 99,644 Lease liabilities ​ ​ 9,515 ​ ​ 7,861 Intangible assets ​ 1,702 ​ 770 Interest carryforwards ​ ​ 1,597 ​ ​ — Accrued expenses and other current liabilities ​ ​ 1,118 ​ ​ 628 Property, plant and equipment ​ 1,072 ​ 761 Derivative financial instrument ​ ​ 661 ​ ​ - Deferred revenue ​ — ​ 6,676 Gross deferred tax asset ​ $ 174,279 ​ $ 116,340 Less valuation allowance ​ (150,113) ​ (109,856) Net deferred tax asset ​ $ 24,166 ​ $ 6,484 Right-of-use asset ​ ​ (7,702) ​ ​ (6,484) Prepaid expenses ​ ​ (45) ​ ​ — Deferred tax liability ​ $ (7,747) ​ $ (6,484) Net deferred tax asset ​ $ 16,419 ​ $ — ​ Changes in the valuation allowance were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) January 1, ​ $ 109,856 ​ $ 85,100 ​ $ 93,682 Changes related to reduction of deferred revenue recorded in equity upon implementation of ASC 606 Revenue recognition as of January 1, 2018 ​ ​ — ​ ​ — ​ ​ (6,229) Changes recorded in profit and loss ​ ​ 30,568 ​ ​ 25,583 ​ ​ 19,207 Increase/(reduction) related to 2020, 2019 and 2018 Dutch tax reforms ​ 18,287 ​ 4,059 ​ (15,670) Release of valuation allowance related to expected current year and future periods recorded in profit and loss ​ ​ (16,419) ​ ​ — ​ ​ — Other changes including currency translation effects ​ 7,821 ​ (4,886) ​ (5,890) December 31, ​ $ 150,113 ​ $ 109,856 ​ $ 85,100 ​ Included within changes recorded in profit and loss for the year ended December 31, 2020 are benefits of $1.2 million from the utilization of U.S. net operating loss carryforwards ($0.8 million for the year ended December 31, 2019 and $0.9 million for the year ended December 31, 2018). ​ The valuation allowance as of December 31, 2020 is primarily related to net operating loss carryforwards in the Netherlands that, in the judgment of management, are not more-likely than-not to be realized. In addition, the valuation allowance as of December 31, 2019 included deferred tax assets for net operating loss carryforwards and temporary differences in the United States of America. Management considered projected future taxable income and tax-planning strategies in making this assessment. A valuation allowance will be recorded against deferred tax assets if it is more likely than not that some or all the deferred tax assets will not be realized. ​ Netherlands ​ The Company determined that in accordance with Dutch tax law it would recognize the CSL Behring License Revenue as well as the License Fees as taxable results as of the date on which the Company is contractually entitled to receive (or obligated to make) a payment under the CSL Behring Agreement. The Company expects to continue to incur taxable losses in the Netherlands except for the period in which it would receive the $450.0 million upfront payment under the CSL Behring Agreement. In the event that the Company recognizes the $450.0 million upfront payment in 2021, such payment is expected to be subject to Dutch corporate income tax at a rate of 25.0%. However, the Company does not expect that it will be required to pay any income taxes in the period in which it recognizes the $450.0 million upfront payment as taxable revenue, as such payment is not expected to exceed the net operating losses that it carries forward in the Netherlands. The Company specifically assessed the impact of the CSL Behring agreement with respect to retaining a full valuation allowance as of December 31, 2020. Closing of the CSL Behring Agreement is contingent on the successful completion of reviews under the antitrust laws in the United States, Australia, and the United Kingdom. The transactions have not closed as of December 31, 2020 as the Company received a Second Request from the United States Federal Trade Commission, on January 4, 2021. Closing of the transaction is dependent on the timing, extent, and result of the Second Request. In its assessment of whether or not it was more likely than not that the Company’s deferred tax assets in the Netherlands will be realized, the Company considered all relevant facts and circumstances, including similar regulatory reviews as well as the five-year cumulative losses reported by the Company in the Netherlands. The Company concluded that it should continue to record a full valuation allowance as of December 31, 2020 in relation to its Dutch net operating loss carryforwards. ​ A portion of the valuation allowance for deferred tax assets relates to follow-on offering costs. Any subsequently recognized tax benefits will be credited directly to contributed capital. As of December 31, 2020, that amount was $7.7 million ($6.9 million as of December 31, 2019). The change is attributable to changes in the foreign currency rate. ​ The Dutch corporate tax rate for fiscal years 2018, 2019 and 2020 was 25%. During the years 2018 and 2019, the Dutch government enacted various changes to the corporate income tax rate applicable to future fiscal years. In September 2020, further changes were enacted that retain the corporate rate at 25% from 2021 onwards. ​ A tax reform in December 2018 limited the carryforward of tax losses arising from January 1, 2019, to six years after the end of the respective period. Tax losses incurred prior to this date continue to expire nine years after the end of the respective period. ​ As of December 31, 2020, new loss compensation rules were accepted by the Dutch Senate. However, the bill includes a provision that the new compensation rules will be effective by a separate Governmental Decree, which has not been introduced as of December 31, 2020. Hence, the new loss compensation rules are not enacted as of December 31, 2020. If enacted, the rules allow losses to be carried forward indefinitely, but from fiscal year 2022 onwards would limit offsetting taxable profit in excess of EUR 1.0 million to 50% of the taxable profit. ​ The Dutch fiscal unity as of December 31, 2020 has an estimated $588.2 million (2019: $414.0 million; 2018: $311.7 million) of taxable losses that can be offset in the following six ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 2022 2023 2024 2025-2027 ​ ​ (in thousands) Loss expiring ​ $ 15,206 ​ $ 25,878 ​ $ 25,202 ​ $ — ​ $ 521,931 ​ The fiscal periods after 2017 are still open for inspection by the Dutch tax authorities. ​ United States of America ​ The federal corporate tax rate in the U.S. is 21%. In addition, the Company is subject to state taxes resulting in a combined tax rate of 27.32% for its U.S. operation. As of December 31, 2020, an estimated $42.3 million of net operating losses remain to be carried forward. These losses will expire between 2035 and 2037. ​ The Company’s U.S. operations generated taxable income in the fiscal years 2018, 2019 and 2020. Based on the current design of the Company’s worldwide operations, the Company expects to continue to generate taxable income in the U.S. during the foreseeable future. As of December 31, 2020, the Company considers it more likely than not that it will utilize its net deferred tax assets in the U.S. and therefore released the remaining valuation allowance of $16.4 million through profit and loss as of this date. ​ Under the provision of the Internal Revenue Code, the U.S. net operating losses may become subject to an annual limitation in the event of certain cumulative exchange in the ownership interest of significant shareholders over a three-year period in excess of 50 percent, as defined under Section 382 and 383 of the Internal Revenue Code. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation. ​ The fiscal periods after 2017 are still open for inspection by the Internal Revenue Service. The Company is currently not under examination by the IRS for any tax years.

Basic and diluted earnings per

Basic and diluted earnings per share	12 Months Ended
	Dec. 31, 2020
Basic and diluted earnings per share
Basic and diluted earnings per share	​ 15. Basic and diluted earnings per share ​ Diluted earnings per share is calculated by adjusting the weighted average number of ordinary shares outstanding, assuming conversion of all potentially dilutive ordinary shares. As the Company has incurred a loss in the years presented, all potentially dilutive ordinary shares would have an antidilutive effect, if converted, and thus have been excluded from the computation of loss per share. The shares are presented without giving effect to the application of the treasury method or exercise prices that would be above the share price as of December 31, 2020, December 31, 2019, and December 31, 2018, respectively. In addition, the BMS warrants were not exercisable as of December 31, 2019, and December 31, 2018, since this would have required the prior designation of Collaboration Targets by BMS. This would generally have resulted in a lower number of potentially dilutive ordinary shares as some stock option grants as well as the BMS warrants would have been excluded. ​ The potentially dilutive ordinary shares are summarized below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 ​ 2018 ​ ​ (ordinary shares) BMS warrants (derecognized as of December 1, 2020 - see Note 4, "Fair value measurement") ​ — ​ 8,893,000 ​ 8,575,000 Stock options under 2014 Plans ​ 2,659,279 ​ 2,683,104 ​ 2,673,712 Non-vested RSUs and earned PSUs ​ 679,958 ​ 850,252 ​ 789,490 Stock options under previous option plan ​ 14,000 ​ 14,000 ​ 32,567 Hercules warrants (exercised February 1, 2019) ​ — ​ — ​ 37,175 Employee share purchase plan ​ 560 ​ 485 ​ 1,012 Total potential dilutive ordinary shares ​ 3,353,797 ​ 12,440,841 ​ 12,108,956 ​

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and contingencies
Commitments and contingencies	16. ​ In the course of its business, the Company enters as a licensee into contracts with other parties regarding the development and marketing of its pipeline products. Among other payment obligations, the Company is obligated to pay royalties to the licensors based on future sales levels and milestone payments whenever specified development, regulatory and commercial milestones are met. As both future sales levels and the timing and achievement of milestones are uncertain, the financial effect of these agreements cannot be estimated reliably. ​

Related party transaction

Related party transaction	12 Months Ended
	Dec. 31, 2020
Related party transaction
Related party transaction	17. Related party transaction ​ Between June 2015 and December 2020, BMS was considered a related party due to the combination of its equity investment in the Company (December 31, 2020: 2.4 million ordinary shares or 5.3% of outstanding ordinary shares), the warrants as well as the potential obligations arising from the expansion of collaboration targets. On December 1, 2020, the Company entered into the amended BMS CLA. All transactions subsequent to the effective date of the amended BMS CLA are considered to no longer be with a related party due to the elimination of the potential obligations related to additional Collaboration Targets (see Note 3 “Collaboration arrangements and concentration of credit risk”) as well as the elimination of the BMS warrants (see Note 4, “Fair value measurement”). ​ On September 14, 2020, the Company appointed Ricardo Dolmetsch, Ph.D. as President, Research and Development. Dr. Dolmetsch succeeded Sander van Deventer, M.D., Ph.D., the former Executive Vice President, Research and Product Development. On August 25, 2020, the Company entered into a separation agreement with Robert Gut, M.D., Ph.D., pursuant to which Dr. Gut transitioned from his role as Chief Medical Officer on October 14, 2020, to be appointed a non-executive director of the Board of Directors. On December 1, 2020, at an extraordinary general meeting, the Company’s shareholders voted to approve the appointment of Dr. Gut as a non-executive director on the Board of Directors. Dr. Gut had previously been appointed as a non-executive director on the Board of Directors on June 13, 2018 by the Company’s shareholders and had resigned as a non-executive director on August 20, 2018, to be appointed as the Company’s Chief Medical Officer. On October 24, 2018, at an extraordinary general meeting, the Company’s shareholders voted to approve the appointment of Dr. Gut as an executive director on the Board of Directors. ​ On June 17, 2020, the Company’s shareholders voted to approve the appointment of Leonard E. Post, Ph.D., as a non-executive director of the Board of Directors. Dr. Post replaced Dr. David Schaffer, whose term as a non-executive director of the Board of Directors ended on the same date. Dr. Post has also assumed the role of chair of the Company’s Research and Development Committee of the Board of Directors. ​ On August 20, 2019, the Company promoted Alex Kuta, Ph.D., to Executive Vice President, Operations. Dr. Kuta, in addition to regulatory affairs, became responsible for global quality as well as GMP manufacturing at the Company’s facility in Lexington, Massachusetts. As of the same date Sander van Deventer, M.D., Ph.D., was promoted to Executive Vice President, Research and Product Development, and Dr. van Deventer, in addition to his responsibilities for research, also became responsible for the Company’s product development. As a result of these changes Scott McMillan, Ph.D. retired from uniQure. The employment of Dr. van Deventer terminated on September 14, 2020. ​ In August 2019, the Company entered into an Amended and Restated Agreement Collaboration and License Agreement (“Amended CLA”) as well as an additional new Collaboration and License Agreement (“New CLA”) with its related party 4DMT Molecular Therapeutics, Inc. (“4DMT”). In the Amended CLA, the Company received from 4DMT an exclusive, sublicensable, worldwide license under certain 4DMT intellectual property rights to research, develop, make, use, and commercialize previously selected Adeno-associated virus (“AAV”) capsid variants and certain associated products using 4DMT proprietary AAV technology for delivery of gene therapy constructs to cells in the central nervous system and the liver (“the Field”). In the New CLA, the parties agreed to research and develop, at 4DMT’s cost, new AAV capsid variants using 4DMT proprietary AAV technology for delivery of up to six additional transgene constructs in the Field that will be selected by the Company. As of June 2020, 4DMT is no longer considered a related party as a result of David Schaffer no longer being a non-executive member of the Company’s Board of Directors. ​

Subsequent events

Subsequent events	12 Months Ended
	Dec. 31, 2020
Subsequent events
Subsequent events	18. Subsequent events ​ Amendment Loan Facility ​ As of December 31, 2020, a $35.0 million term loan was outstanding in accordance with the 2018 Amended Facility between the Company and Hercules. ​ On January 29, 2021, the Company and Hercules amended the Company’s loan facility with Hercules Capital Inc. entered, (“2021 Amended Facility”). Pursuant to the 2021 Amended Facility, Hercules agreed to the 2021 Term Loan, increasing the aggregate principal amount of the term loan facility from $35.0 million to $135.0 million. On January 29, 2021, the Company drew down $35.0 million of the 2021 Term Loan. The Company may draw down the remaining $65.0 million under the 2021 Term Loan in a series of one or more advances of not less than $20.0 million each until December 15, 2021. Advances under the 2021 Term Loan bear interest at a rate equal to the greater of (i) 8.25% or (ii) 8.25% plus the prime rate, less 3.25% per annum. The principal balance and all accrued but unpaid interest on advances under 2021 Term Loan is due on June 1, 2023, which date may be extended by the Company by up to two twelve-month periods. Advances under the 2021 Term Loan may not be prepaid until six months after the Closing Date, following which the Company may prepay all such advances without charge. ​ In addition to the 2021 Term Loan, the amendment also extends the interest-only payment period of the previously funded $35.0 million term loan from January 1, 2022 to June 1, 2023. ​ The Company paid a $0.4 million facility charge on January 29, 2021. End of term charges in respect of advances under the 2021 Term Loan range from 1.65% to 6.85% depending on the maturity date.

Summary of significant accoun_2

Summary of significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2020
Summary of significant accounting policies
Basis of preparation	2.1 Basis of preparation ​ The Company prepared its consolidated financial statements in compliance with generally accepted accounting principles in the United States (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to authoritative U.S. GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). ​ The consolidated financial statements have been prepared under the historical cost convention, except for derivative financial instruments and contingent consideration, which are recorded at fair value through profit or loss. ​ The consolidated financial statements are presented in U.S. dollars, except where otherwise indicated. Transactions denominated in currencies other than U.S. dollars are presented in the transaction currency with the U.S. dollar amount included in parenthesis, converted at the foreign exchange rate as of the transaction date. ​ The consolidated financial statements presented have been prepared on a going concern basis based on the Company’s cash and cash equivalents as of December 31, 2020 and the Company’s budgeted cash flows for the twelve months following the issuance date.
Use of estimates	2.2 ​ The preparation of consolidated financial statements, in conformity with U.S. GAAP and Securities and Exchange Commission (“SEC”) rules and regulations, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the consolidated financial statements and reported amounts of revenues and expenses during the reporting period. Estimates and assumptions are primarily made in relation to the treatment of the commercialization and license agreement entered into between the Company and CSL Behring LLC (“CSL Behring Agreement”), the December 1, 2020, amendment (“amended BMS CLA”) of the 2015 collaboration and license agreement (“BMS CLA”) between the Company and Bristol-Myers Squibb (“BMS”), share-based payments, valuation allowances for deferred tax assets, and accounting for operating leases under ASC 842. If actual results differ from the Company’s estimates, or to the extent these estimates are adjusted in future periods, the Company’s results of operations could either benefit from, or be adversely affected by, any such change in estimate.
Accounting policies	2.3 ​ The principal accounting policies applied in the preparation of these consolidated financial statements are set out below. These policies have been consistently applied to all the years presented, unless otherwise stated.
Consolidation	2.3.1 ​ The consolidated financial statements comprise the financial statements of the Company and its subsidiaries. Subsidiaries are all entities over which the Company has a controlling financial interest either through variable interest or through voting interest. Currently, the Company has no involvement with variable interest entities. ​ Inter-company transactions, balances, income, and expenses on transactions between uniQure entities are eliminated in consolidation. Profits and losses resulting from inter-company transactions that are recognized in assets are also eliminated. Accounting policies of subsidiaries have been changed where necessary to ensure consistency with the policies adopted by the Company.
Current versus non-current classification	2.3.2 ​ The Company presents assets and liabilities in the consolidated balance sheets based on current and non-current classification. ​ The term current assets is used to designate cash and other assets, or resources commonly identified as those that are reasonably expected to be realized in cash or sold or consumed during the normal operating cycle of the business. The Company’s normal operating cycle is twelve months. All other assets are classified as non-current. ​ The term current liabilities is used principally to designate obligations whose liquidation is reasonably expected to require the use of existing resources properly classifiable as current assets, or the creation of other current liabilities. Current liabilities are expected to be settled in the normal operating cycle. The Company classifies all other liabilities as non-current. ​ Deferred tax assets and liabilities are classified as non-current assets and liabilities, if any.
Foreign currency translation	2.3.3 ​ The functional currency of the Company and each of its entities (except for uniQure Inc.) is the euro (€). This represents the currency of the primary economic environment in which the entities operate. The functional currency of uniQure Inc. is the U.S. dollar ($). The consolidated financial statements are presented in U.S. dollars. ​ Foreign currency transactions are measured and recorded in the functional currency using the exchange rates prevailing at the dates of the transactions. Foreign exchange gains and losses resulting from the settlement of such transactions and from the re-measurement of monetary assets and liabilities denominated in foreign currencies at exchange rates prevailing at balance sheet date are recognized in profit and loss. ​ Upon consolidation, the assets and liabilities of foreign operations are translated into the functional currency of the shareholding entity at the exchange rates prevailing at the balance sheet date; items of income and expense are translated at monthly average exchange rates. The consolidated assets and liabilities are translated from uniQure N.V.’s functional currency, euro, into the reporting currency U.S. dollar at the exchange rates prevailing at the balance sheet date; items of income and expense are translated at monthly average exchange rates. Issued capital and additional paid-in capital are translated at historical rates with differences to the balance sheet date rate recorded as translation adjustments in other comprehensive income / loss. The exchange differences arising on translation for consolidation are recognized in “accumulated other comprehensive income / loss”. On disposal of a foreign operation, the component of other comprehensive income / loss relating to that foreign operation is recognized in profit or loss.
Fair value measurement	2.3.4 ​ The Company measures certain assets and liabilities at fair value, either upon initial recognition or for subsequent accounting or reporting. ASC 820, Fair Value Measurements and Disclosures ​ ● Level 1 - Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company can access at the measurement date. ​ ● Level 2 - Valuations based on quoted prices for similar assets or liabilities in markets that are not active or models for which the inputs are observable, either directly or indirectly. ​ ● Level 3 - Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and are unobservable. ​ To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. ​ Items measured at fair value on a recurring basis include financial instruments and contingent consideration (Note 4, “Fair value measurement”). The carrying amount of cash and cash equivalents, accounts receivable from collaborators, prepaid expenses, other assets, accounts payable, accrued expenses and other current liabilities reflected in the consolidated balance sheets approximate their fair values due to their short-term maturities.
Notes to the consolidated statements of cash flows	2.3.5 ​ The consolidated statements of cash flows have been prepared using the indirect method. The cash disclosed in the consolidated statements of cash flows is comprised of cash and cash equivalents. Cash and cash equivalents include bank balances, demand deposits and other short-term highly liquid investments (with maturities of less than three months at the time of purchase) that are readily convertible into a known amount of cash and are subject to an insignificant risk of fluctuation in value. ​ Cash flows denominated in foreign currencies have been translated at the average exchange rates. Exchange differences, if any, affecting cash and cash equivalents are shown separately in the consolidated statements of cash flows. Interest paid and received, and income taxes are included in net cash (used in) provided by operating activities.
Segment information	2.3.6 ​ Operating segments are identified as a component of an enterprise for which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions on how to allocate resources and assess performance. The Company views its operations and manages its business as one operating segment, which comprises the discovery, development, and commercialization of innovative gene therapies.
Net loss per share	2.3.7 ​ The Company follows the provisions of ASC 260, Earnings Per Share ​ Diluted net loss per share reflects the dilution that would occur if share options or warrants to issue ordinary shares were exercised, or performance or restricted share units were distributed. However, potential ordinary shares are excluded if their effect is anti-dilutive. The Company currently has no dilutive securities due to the net loss position and as such, basic and diluted net loss per share are the same for the periods presented.
Impairment of long-lived assets	2.3.8 ​ Long-lived assets, which include property, plant, and equipment and finite-lived intangible assets, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying value of an asset or asset group may not be recoverable. Right-of-use assets are also reviewed for impairment in accordance with ASC 360. The recoverability of the carrying value of an asset or asset group depends on the successful execution of the Company’s business initiatives and its ability to earn sufficient returns on approved products and product candidates. When such events or changes in circumstances occur, the Company assesses recoverability by determining whether the carrying value of such assets will be recovered through the undiscounted expected future cash flows. If the future undiscounted cash flows are less than the carrying amount of these assets, the Company recognizes an impairment loss based on the excess of the carrying value over the fair value of the assets. Fair value is determined through various valuation techniques, including discounted cash flow models, quoted market values, and third-party independent appraisals, as considered necessary. ​ Goodwill is not amortized but is evaluated for impairment within the Company’s single reporting unit on an annual basis, during the fourth quarter, or more frequently if an event occurs or circumstances change that would more-likely-than-not reduce the fair value of the Company’s reporting unit below its carrying amount. The Company performs the same quantitative analysis discussed above for long-lived assets and finite-lived intangible assets.
Property, plant, and equipment	2.3.9 ​ Property, plant, and equipment is comprised mainly of laboratory equipment, leasehold improvements, construction-in-progress (“CIP”) and office equipment. All property, plant and equipment is stated at cost less accumulated depreciation. CIP consists of capitalized expenses associated with construction of assets not yet placed into service. Depreciation commences on CIP once the asset is placed into service based on its useful life determined at that time. ​ Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed as incurred. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss on the transaction is recognized in the consolidated statements of operations and comprehensive loss. ​ Depreciation is calculated using the straight-line method over the estimated useful lives of the assets (or in the case of leasehold improvements a shorter lease term), which are as follows: ​ ​ ​ ​ · Between 10 – 15 years · ​ 5 years · ​ Between 3 – 5 years
Leases	2.3.10 ​ The Company adopted ASC 842 using the modified retrospective approach with an effective date as of the beginning of the Company’s fiscal year, January 1, 2019, to operating leases that existed on that date. Comparative financial information related to profit and loss and cash flows for the twelve-month period ended December 31, 2018, was not recast under the new standard, and continues to be presented under ASC 840. ​ The Company measured lease liabilities at the present value of the future lease payments as of January 1, 2019. The Company used an incremental borrowing rate to discount the lease payments. The Company derived the discount rate, adjusted for differences such as in the term and payment patterns, from the Company’s loan from Hercules Technology Growth Capital, Inc (“Hercules Capital”), which was refinanced immediately prior to the January 1, 2019 adoption date in December 2018. The right-of-use asset is valued at the amount of the lease liability reduced by the remaining December 31, 2018 balance of lease incentives received. The lease liability is subsequently measured at the present value of the future lease payments as of the reporting date with a corresponding adjustment to the right-to-use asset. Absent a lease modification, the Company will continue to utilize the January 1, 2019, incremental borrowing rate. ​ ​ The financial results for the years ended December 31, 2020 and 2019 are presented in accordance with ASC 842, while the financial results for the year ended December 31, 2018 are presented in accordance with the Company’s historical accounting policy based on ASC 840.
Other (non) current assets	2.3.11 ​ Deposits paid are either presented as other current assets or as other non-current assets based on duration of the underlying contractual arrangement. Deposits are classified as restricted cash and primarily relate to facility leases. ​ Contract assets are presented in other current assets or as other non-current assets based on the timing of the right to consideration.
Prepaid expenses	2.3.12 ​ Prepaid expenses are amounts paid in the period, for which the benefit has not been realized, and include payments made for insurance and research and clinical contracts. The related expense will be recognized in the subsequent period as incurred.
Accounts receivables	2.3.13 ​
Accounts payable and accrued expenses	2.3.14 ​ Accounts payables are invoiced amounts related to obligations to pay for goods or services that have been acquired in the ordinary course of business from suppliers. Accounts payables are recognized at the amounts invoiced by suppliers. ​ Accrued expenses are recognized for goods or services that have been acquired in the ordinary course of business. ​ Contract liabilities are presented in accounts payable and accrued expenses.
Long-term debt	2.3.15 ​ Long-term debt is initially recognized at cost and presented net of original issue discount or premium and debt issuance costs on the consolidated balance sheets. Amortization of debt discount and debt issuance costs is recognized as interest expense in profit and loss over the period of the debt, using the effective interest rate method.
Pensions and other post-retirement benefit plans	2.3.16 Pensions and other post-retirement benefit plans ​ The Company has a defined contribution pension plan for all employees at its Amsterdam facility in the Netherlands, which is funded by the Company through payments to an insurance company, with individual accounts for each participants’ assets. The Company has no legal or constructive obligation to pay further contributions if the plan does not hold sufficient assets to pay all employees the benefits relating to services rendered in the current and prior periods. The contributions are expensed as incurred. Prepaid contributions are recognized as an asset to the extent that a cash refund or a reduction in the future payments is available. ​ Starting in 2016, the Company adopted a qualified 401(k) Plan for all employees at its Lexington facility in the USA, which offers both a pre-tax and post-tax (Roth) component. Employees may contribute up to 50% of their pre-tax compensation, which is subject to IRS statutory limits for each calendar year. The Company matches $0.50 for every $1.00 contributed to the plan by participants up to 6% of base compensation. Employer contributions are recognized as they are contributed, as long as the employee is rendering services in that period. If employer contributions are made in periods after an individual retires or terminates, the estimated cost is accrued during the employee’s service period.
Share-based compensation	2.3.17 ​ The Company accounts for its share-based compensation awards in accordance with ASC 718, Compensation-Stock Compensation. ​ All the Company’s share-based compensation plans for employees are equity-classified. ​ ASC 718 requires all share-based compensation to employees, including grants of employee options, restricted share units, performance share units and modifications to existing instruments, to be recognized in the consolidated statements of operations and comprehensive loss based on their grant-date fair values, net of an estimated forfeiture rate, over the requisite service period. Forfeitures of employee options are recognized as they occur. The requirements of ASC 718 are also applied to nonemployee share-based payment transactions except for specific guidance on certain inputs to an option-pricing model and the attribution of cost. ​ The Company uses a Hull & White option model to determine the fair value of option awards. The model captures early exercises by assuming that the likelihood of exercises will increase when the share-price reaches defined multiples of the strike price. This analysis is performed over the full contractual term.
Revenue recognition	2.3.18 Revenue recognition ​ The Company primarily generates revenue from its collaboration, research, and license agreements with its collaboration partner BMS for the development and commercialization of product candidates. The Company initially entered into these agreements in 2015 and amended them in 2020. ​ On January 1, 2018, the Company adopted new revenue recognition policies in accordance with ASC 606 using the modified retrospective approach. The Company evaluated the initial BMS CLA and determined that its performance obligations were as follows: ​ ● Providing pre-clinical research activities (“Collaboration Revenue”); ● Providing clinical and commercial manufacturing services for products (“Manufacturing Revenue”); and ● Providing access to its technology and know-how in the field of gene therapy as well as actively contributing to the target selection, the collaboration as a whole, the development during the target selection, the pre-clinical and the clinical phase through participating in joint steering committee and other governing bodies (“License Revenue”). As further discussed in Note 3, “Collaboration arrangements and concentration of credit risk”, as a result of the December 2020 amended BMS CLA, the Company’s performance obligation related to License Revenues was materially completed as of the date of the amendment effective date of December 1, 2020. The Company may still be required to provide pre-clinical research activities or clinical and commercial manufacturing services when BMS exercises its options for those services. ​ License Revenue ​ Until the December 2020 amendment of the BMS CLA the Company recognized License Revenue over the expected performance period based on its measure of progress towards the completion of certain activities related to its services. Following the December 2020 amendment of the BMS CLA the Company’s performance was materially completed and it had satisfied its performance obligation (see Note 3, “Collaboration arrangements and concentration of credit risk”, for a detailed discussion). ​ Collaboration and Manufacturing Revenue ​ The Company recognizes Collaboration Revenues associated to optional work orders it receives from BMS to provide analytical development and process development activities that are reimbursable by BMS in accordance with the BMS CLA as well as the amended BMS CLA. ​ BMS and the Company entered into a Master Clinical Supply Agreement in April 2017 for the Company to supply gene therapy products during the clinical phase as well as into a binding term sheet to supply gene therapy products during the commercial phase to BMS. In December 2020, BMS and the Company also entered into a Research Supply Agreement. Revenues from product sales will be recognized when earned. The Company will provide these services as it receives optional work orders from BMS in relation to such services.
Other income, other expense	​ 2.3.19 ​ The Company receives certain government and regional grants, which support its research efforts in defined projects, and include contributions towards the cost of research and development. These grants generally provide for reimbursement of approved costs incurred as defined in the respective grants and are deferred and recognized in the statements of operations and comprehensive loss over the period necessary to match them with the costs they are intended to compensate, when it is probable that the Company has complied with any conditions attached to the grant and will receive the reimbursement. ​ The Company’s other income also consists of income from the subleasing of the Amsterdam facility while other expense consists of expenses incurred in relation to the subleasing income. ​
Research and development expenses	2.3.20 ​ Research and development costs are expensed as incurred. Research and development expenses generally consist of laboratory research, clinical trials, statistical analysis, and report writing, regulatory compliance costs incurred with clinical research organizations and other third-party vendors (including post-approval commitments to conduct consistency and comparability studies). In addition, research and development expenses consist of start-up and validation costs related to the Company’s Lexington facility and the development and improvement of the Company’s manufacturing processes and methods. Furthermore, research and development costs include costs of materials and costs of intangible assets purchased from others for use in research and development activities. The costs of intangibles that are purchased from others for a particular research and development project and that have no alternative future uses (in other research and development projects or otherwise) are expensed as research and development costs at the time the costs are incurred or at the time when no alternative future use is identified.
Income taxes	2.3.21 ​ Income taxes are recorded in accordance with ASC 740, Income Taxes ​ The benefits of tax positions are recognized only if those positions are more likely than not, based on the technical merits, to be sustained upon examination. Recognized tax positions are measured at the largest amount of tax benefit that is greater than 50 percent likely of being realized upon settlement. The determination as to whether the tax benefit will more-likely-than-not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2020, and 2019, the Company did not have any significant unrecognized tax benefits.
Recent accounting pronouncements	2.3.22 Recently Adopted Accounting Pronouncements ​ ASU 2018-13: Fair Value Measurement ​ In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820) which modifies the disclosure requirements on fair value measurements. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019, which for the Company was January 1, 2020. The new disclosure requirements for changes in unrealized gains and losses in other comprehensive income for recurring Level 3 measurements, the range and weighted average of significant unobservable inputs and the amended requirements for the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments should be applied retrospectively. ASU 2018-13 did not have a material impact on the Company’s consolidated financial statements. ​ Recent Accounting Pronouncements Not Yet Effective ​ None.

Summary of significant accoun_3

Summary of significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2020
Summary of significant accounting policies
Schedule of estimated useful lives of depreciable property, plant and equipment	​ ​ ​ ​ · Between 10 – 15 years · ​ 5 years · ​ Between 3 – 5 years

Collaboration arrangements an_2

Collaboration arrangements and concentration of credit risk (Tables)	12 Months Ended
	Dec. 31, 2020
Collaboration arrangements and concentration of credit risk
Schedule of collaboration and license revenue	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 ​ ​ 2019 ​ ​ 2018 ​ ​ (in thousands) Bristol Myers Squibb $ 37,514 ​ $ 7,281 ​ $ 11,284 Total $ 37,514 ​ $ 7,281 ​ $ 11,284
Schedule of amounts owed in relation to collaboration	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Bristol Myers Squibb ​ $ 4,536 ​ $ 947 Total ​ $ 4,536 ​ $ 947

Fair value measurement (Tables)

Fair value measurement (Tables)	12 Months Ended
	Dec. 31, 2020
Fair value measurement
Schedule of changes in Level 3 items	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivative ​ ​ ​ ​ ​ Contingent ​ financial ​ ​ ​ ​ consideration instruments Total ​ ​ (in thousands) Balance at December 31, 2017 ​ $ 3,964 ​ $ 1,635 ​ $ 5,599 Net gains recognized in profit or loss ​ ​ (3,846) ​ ​ (208) ​ ​ (4,054) Currency translation effects ​ ​ (118) ​ ​ (52) ​ ​ (170) Balance at December 31, 2018 ​ $ — ​ $ 1,375 ​ $ 1,375 Net losses recognized in profit or loss ​ ​ — ​ ​ 2,530 ​ ​ 2,530 Exercise of Hercules warrants ​ ​ — ​ ​ (770) ​ ​ (770) Currency translation effects ​ ​ — ​ ​ (60) ​ ​ (60) Balance at December 31, 2019 ​ $ — ​ $ 3,075 ​ $ 3,075 Net gains recognized in profit or loss ​ ​ — ​ ​ (2,300) ​ ​ (2,300) Derecognition of warrants ​ ​ — ​ ​ (796) ​ ​ (796) Recognition of derivative financial liability of CoC-payment ​ ​ — ​ ​ 2,613 ​ ​ 2,613 Currency translation effects ​ ​ — ​ ​ 53 ​ ​ 53 Balance at December 31, 2020 ​ $ — ​ $ 2,645 ​ $ 2,645

Property, plant and equipment_2

Property, plant and equipment, net (Tables)	12 Months Ended
	Dec. 31, 2020
Property, plant and equipment, net
Schedule of property, plant and equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Leasehold improvements ​ $ 37,849 ​ $ 34,611 Laboratory equipment ​ ​ 22,106 ​ ​ 18,232 Office equipment ​ ​ 5,025 ​ ​ 4,212 Construction-in-progress ​ ​ 2,574 ​ ​ 341 Total property, plant, and equipment ​ ​ 67,554 ​ ​ 57,396 Less accumulated depreciation ​ ​ (35,226) ​ ​ (28,625) Property, plant and equipment, net ​ $ 32,328 ​ $ 28,771
Summary of long-lived assets by geographic region	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Lexington, Massachusetts (United States of America) ​ $ 15,949 ​ $ 15,490 Amsterdam (the Netherlands) ​ 16,379 ​ 13,281 Total ​ $ 32,328 ​ $ 28,771

Right-of-use asset and lease _2

Right-of-use asset and lease liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Right-of-use asset and lease liabilities
Schedule of lease cost, balance sheet and cash flow information	​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2020 2019 ​ ​ (in thousands) Operating lease cost ​ $ 5,052 ​ $ 4,474 Variable lease cost ​ ​ 607 ​ ​ 507 Sublease income ​ ​ (904) ​ ​ (1,053) Total lease cost ​ $ 4,755 ​ $ 3,928 ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Assets ​ ​ ​ ​ ​ ​ Operating lease right-of-use assets ​ $ 26,086 ​ ​ 26,797 Liabilities ​ ​ ​ ​ ​ ​ Current ​ ​ ​ ​ ​ ​ Current operating lease liabilities ​ ​ 5,524 ​ ​ 5,865 Non-current ​ ​ ​ ​ ​ ​ Non-current operating lease liabilities ​ ​ 30,403 ​ ​ 31,133 Total lease liabilities ​ $ 35,927 ​ ​ 36,998 ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2020 2019 ​ ​ (in thousands) Operating cash flows for operating leases (1) ​ $ 5,769 ​ $ 4,717 ​ (1) The Company has received $1.5 million of landlord incentive payments for the year ended December 31, 2019, which are not included in the cash paid amounts.)
Summary of aggregate rent expense	​ ​ ​ ​ ​ ​ Year ended December 31, ​ 2018 ​ ​ (in thousands) Rent expense - Lexington ​ $ 1,583 Rent expense - Amsterdam ​ ​ 1,667 Total lease cost ​ $ 3,250 ​
Schedule of undiscounted cash flows and minimum lease payments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Lexington ​ Amsterdam (1) ​ Total ​ (in thousands) 2021 $ 3,455 ​ $ 2,069 ​ $ 5,524 2022 ​ 3,552 ​ ​ 2,069 ​ ​ 5,621 2023 ​ 3,650 ​ ​ 2,069 ​ ​ 5,719 2024 ​ 4,146 ​ ​ 2,069 ​ ​ 6,215 2025 ​ 4,465 ​ ​ 2,069 ​ ​ 6,534 Thereafter ​ 16,279 ​ ​ 12,239 ​ ​ 28,518 Total lease payments $ 35,547 ​ $ 22,584 ​ $ 58,131 ​ ​ ​ ​ ​ ​ ​ ​ ​ Less: amount of lease payments representing interest payments ​ (12,576) ​ ​ (9,628) ​ ​ (22,204) Present value of lease payments ​ 22,971 ​ ​ 12,956 ​ ​ 35,927 Less: current operating lease liabilities ​ (3,455) ​ ​ (2,069) ​ ​ (5,524) Non-current operating lease liabilities $ 19,516 ​ $ 10,887 ​ $ 30,403 (1) Payments are due in EUR and have been translated at the foreign exchange rate as of December 31, 2020, of $1.23 / €1.00)

Intangible assets (Tables)

Intangible assets (Tables)	12 Months Ended
	Dec. 31, 2020
Intangible assets
Schedule of finite-lived intangible assets	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Licenses ​ $ 5,660 ​ $ 8,317 Less accumulated amortization and impairment ​ ​ (2,299) ​ ​ (2,890) Licenses, net ​ $ 3,361 ​ $ 5,427
Schedule of estimated future amortization expense	​ ​ ​ ​ ​ Years Amount ​ ​ (in thousands) 2021 ​ $ 1,277 2022 ​ 427 2023 ​ 144 2024 ​ 144 2025 ​ 144 Thereafter ​ 1,225 Total ​ $ 3,361

Accrued expenses and other cu_2

Accrued expenses and other current liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Accrued expenses and other current liabilities
Schedule of accrued expenses and other current liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 2019 ​ ​ (in thousands) Accruals for services provided by vendors-not yet billed ​ $ 8,269 ​ $ 5,425 Personnel related accruals and liabilities ​ ​ 7,687 ​ ​ 7,032 Contract liability (see Note 3. Collaboration arrangements) ​ ​ 2,082 ​ ​ — Total ​ $ 18,038 ​ $ 12,457

Long-term debt (Tables)

Long-term debt (Tables)	12 Months Ended
	Dec. 31, 2020
Long-term debt
Schedule of interest expense	​ ​ ​ ​ ​ Years Amount ​ ​ (in millions) 2020 ​ $ 3.7 2019 ​ 3.7 2018 ​ ​ 2.0
Schedule of aggregate maturities of the loan	​ ​ ​ ​ ​ Years Amount ​ ​ (in thousands) 2021 ​ $ 3,141 2022 ​ 25,002 2023 ​ ​ 14,269 Total ​ $ 42,412

Share-based compensation (Table

Share-based compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based compensation
Schedule of share-based compensation expense by classification included in consolidated statements of operations and comprehensive loss	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Research and development ​ $ 11,965 ​ $ 8,029 ​ $ 3,994 Selling, general and administrative ​ ​ 9,823 ​ ​ 9,439 ​ ​ 6,699 Total ​ $ 21,788 ​ $ 17,468 ​ $ 10,693
Schedule of share-based compensation expense	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Award type ​ ​ ​ ​ ​ ​ ​ ​ ​ Share options ​ $ 11,434 ​ $ 7,896 ​ $ 4,766 Restricted share units ​ ​ 7,364 ​ ​ 4,117 ​ ​ 3,020 Performance share units ​ ​ 2,990 ​ ​ 5,455 ​ ​ 2,907 Total ​ $ 21,788 ​ $ 17,468 ​ $ 10,693
Schedule of unrecognized compensation cost related to unvested awards	​ ​ ​ ​ ​ ​ ​ ​ Unrecognized Weighted average ​ share-based remaining ​ ​ compensation ​ period for ​ ​ expense ​ recognition ​ ​ (in thousands) ​ (in years) Award type ​ ​ ​ ​ ​ Share options ​ $ 23,492 ​ 2.78 Restricted share units ​ ​ 14,489 ​ 2.09 Performance share units ​ ​ 1,763 ​ 1.03 Total ​ $ 39,744 ​ 2.45
Schedule of weighted-average assumptions for fair value of option issued	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended December 31, Assumptions 2020 2019 ​ 2018 Expected volatility ​ 70% ​ 70% - 75% ​ 75% - 80% Expected terms ​ 10 years ​ 10 years ​ 10 years Risk free interest rate ​ 0.76% - 1.44% ​ 1.92% - 2.87% ​ 2.67% - 3.20% Expected dividend yield ​ 0% ​ 0% ​ 0%
Summary of RSUs activity	​ ​ ​ ​ ​ ​ ​ ​ ​ RSU ​ ​ Weighted average ​ ​ Number of ​ grant-date fair ​ ​ ordinary shares ​ value Non-vested at December 31, 2019 ​ 370,830 ​ $ 28.62 Granted ​ 376,799 ​ $ 48.18 Vested ​ (206,881) ​ $ 24.18 Forfeited ​ (73,404) ​ $ 46.41 Non-vested at December 31, 2020 ​ 467,344 ​ $ 43.56 ​ ​ ​ ​ ​ ​ Total weighted average grant date fair value of RSUs granted during the period (in $ millions) ​ ​ ​ $ 18.2 Granted to directors and officers during the period (shares, $ in millions) ​ 158,623 ​ $ 7.4
Summary of PSUs activity	​ ​ ​ ​ ​ ​ ​ ​ ​ PSU ​ ​ Weighted average ​ ​ Number of ​ grant-date fair ​ ​ ordinary shares ​ value Non-vested at December 31, 2019 ​ 479,422 ​ $ 21.17 Granted ​ 91,003 ​ $ 57.56 Vested ​ (354,105) ​ $ 17.44 Forfeited ​ (3,706) ​ $ 57.56 Non-vested at December 31, 2020 ​ 212,614 ​ $ 42.32 ​ ​ ​ ​ ​ ​ Total weighted average grant date fair value of PSUs granted during the period (in $ millions) ​ ​ ​ $ 5.2
2014 Plan
Share-based compensation
Summary of option activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options ​ ​ Number of ​ Weighted average ​ Weighted average ​ Aggregate intrinsic ​ ordinary shares exercise price remaining contractual life value ​ ​ ​ ​ ​ ​ ​ in years ​ ​ (in thousands) Outstanding at December 31, 2019 ​ 2,683,104 ​ $ 21.29 ​ 7.46 ​ $ 135,238 Granted ​ 653,852 ​ $ 49.63 ​ ​ ​ ​ ​ Forfeited ​ (172,548) ​ $ 42.03 ​ ​ ​ ​ ​ Expired ​ (6,451) ​ $ 45.76 ​ ​ ​ ​ ​ Exercised ​ (498,678) ​ $ 14.43 ​ ​ ​ ​ ​ Outstanding at December 31, 2020 ​ 2,659,279 ​ $ 28.13 ​ 7.18 ​ ​ 32,729 Thereof, fully vested and exercisable at December 31, 2020 ​ 1,542,405 ​ $ 18.05 ​ 6.15 ​ ​ 29,161 Thereof, outstanding and expected to vest after December 31, 2020 ​ 1,116,874 ​ $ 42.06 ​ 8.61 ​ ​ 3,568 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Outstanding and expected to vest at December 31, 2019 ​ 1,346,337 ​ $ 28.76 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total weighted average grant date fair value of options issued during the period (in $ millions) ​ ​ ​ $ 18.4 ​ ​ ​ ​ ​ Granted to directors and officers during the period (options, grant date fair value $ in millions) ​ 209,254 ​ $ 5.7 ​ ​ ​ ​ ​ Proceeds from option sales during the period (in $ millions) ​ ​ ​ $ 7.2 ​ ​ ​ ​ ​
Summary of information about weighted average grant-date fair value of options granted	​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average ​ ​ Options ​ grant ‑ date fair value Granted, 2020 653,852 ​ $ 28.08 Granted, 2019 647,526 ​ ​ 23.57 Granted, 2018 937,832 ​ ​ 15.90 Vested, 2020 ​ 713,924 ​ ​ 14.04 Forfeited, 2020 ​ (172,548) ​ ​ 24.63
Summary of summarizes information about the weighted average grant-date fair value of options outstanding and expected to vest	​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted average ​ ​ Options ​ grant ‑ date fair value Outstanding and expected to vest, 2020 1,116,874 ​ $ 24.25 Outstanding and expected to vest, 2019 1,346,337 ​ ​ 17.05
Summary of information about options exercised	​ ​ ​ ​ ​ ​ ​ ​ Exercised ​ ​ ​ ​ during the year ​ Intrinsic value ​ ​ ​ ​ (in thousands) 2020 498,678 ​ $ 11,927 2019 434,665 ​ 17,700 2018 388,203 ​ 7,515
Restricted share units ("RSUs")
Share-based compensation
Summary of information about weighted average grant-date fair value of options granted	​ ​ ​ ​ ​ ​ ​ ​ Granted Weighted average ​ ​ during the year ​ grant ‑ date fair value 2020 376,799 ​ $ 48.18 2019 198,504 ​ ​ 38.63 2018 262,599 ​ ​ 23.61
Summary of information about the total fair value of stock that vested	​ ​ ​ ​ ​ Total fair value ​ (in thousands) 2020 $ 12,156 2019 10,152 2018 8,546
Performance share units ("PSUs")
Share-based compensation
Summary of information about weighted average grant-date fair value of options granted	​ ​ ​ ​ ​ ​ ​ ​ Granted Weighted average ​ ​ during the year ​ grant ‑ date fair value 2020 91,003 ​ $ 57.56 2019 132,362 ​ $ 31.71 2018 — ​ $ —
Summary of information about the total fair value of stock that vested	​ ​ ​ ​ ​ Total fair value ​ (in thousands) 2020 $ 21,852 2019 1,056 2018 1,350

Expenses by nature (Tables)

Expenses by nature (Tables)	12 Months Ended
	Dec. 31, 2020
Expenses by nature
Schedule of operating expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) Employee-related expenses ​ $ 75,926 ​ $ 59,130 ​ $ 46,254 Laboratory and development expenses ​ 35,977 ​ 30,130 ​ 23,596 Office and housing expenses ​ 13,388 ​ 10,588 ​ 7,281 Legal and advisory expenses ​ 17,370 ​ 11,297 ​ 7,748 Depreciation, amortization, and impairment expenses ​ 10,648 ​ 6,669 ​ 12,415 Patent and license expenses ​ 2,899 ​ 1,654 ​ 1,202 Other operating expenses ​ 8,772 ​ 8,813 ​ 1,618 Total ​ $ 164,980 ​ $ 128,281 ​ $ 100,114
Schedule of employee-related expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) Wages and salaries ​ $ 40,919 ​ $ 32,029 ​ $ 26,646 Share-based compensation expenses ​ 21,831 ​ 17,533 ​ 10,708 Consultant expenses ​ 2,423 ​ 2,464 ​ 2,974 Social security costs ​ 4,068 ​ 2,727 ​ 2,231 Health insurance ​ 2,271 ​ 1,933 ​ 1,471 Pension costs - defined contribution plans ​ 1,779 ​ 1,052 ​ 907 Other employee expenses ​ 2,635 ​ 1,392 ​ 1,317 Total ​ $ 75,926 ​ $ 59,130 ​ $ 46,254

Other non-operating income _ _2

Other non-operating income / (expense) (Tables)	12 Months Ended
	Dec. 31, 2020
Other non-operating income / (expense)
Schedule of other non-operating income / (expense)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Other non-operating income: ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivative gains ​ $ 483 ​ $ — ​ $ 208 Total other non-operating income: ​ ​ 483 ​ ​ — ​ ​ 208 Other non-operating expense: ​ ​ ​ ​ ​ ​ ​ ​ ​ Derivative losses ​ ​ — ​ ​ (2,530) ​ ​ — Total other non-operating expense: ​ ​ — ​ ​ (2,530) ​ ​ — Other non-operating income / (expense), net ​ $ 483 ​ $ (2,530) ​ $ 208

Income taxes (Tables)

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income taxes
Schedule of loss before income taxes	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) Dutch operations ​ $ (130,493) ​ $ (111,820) ​ $ (85,721) U.S. operations ​ (10,950) ​ (12,381) ​ 2,646 Foreign operations ​ — ​ — ​ 3 Total ​ $ (141,443) ​ $ (124,201) ​ $ (83,073)
Schedule of income tax benefit / (expense)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) Current tax expense ​ ​ ​ ​ ​ ​ ​ ​ ​ Dutch operations ​ $ — ​ $ — ​ $ — U.S. operations ​ — ​ — ​ — Foreign operations ​ — ​ ​ — ​ (22) Total current tax expense ​ $ — ​ $ — ​ $ (22) Deferred tax benefit / (expense) ​ ​ ​ ​ ​ ​ Dutch operations ​ $ — ​ $ — ​ $ (209) U.S. operations ​ 16,419 ​ — ​ — Foreign operations ​ — ​ — ​ — Total deferred tax benefit / (expense) ​ $ 16,419 ​ $ — ​ $ (209) Total income tax benefit / (expense) ​ $ 16,419 ​ $ — ​ $ (231)
Schedule of reconciliation of statutory income tax rate to effective tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ ​ 2020 ​ 2019 ​ 2018 ​ ​ (in thousands) Loss before income tax income / (expense) for the period ​ $ (141,443) ​ $ (124,201) ​ $ (83,073) Expected income tax benefit at the tax rate enacted in the Netherlands (25%) ​ 35,361 ​ 31,050 ​ 20,768 Difference in tax rates between the Netherlands and the U.S. as well as other foreign countries ​ 247 ​ (495) ​ (106) Release of valuation allowance related to expected future taxable income of U.S. operations ​ ​ 16,419 ​ ​ — ​ ​ — Other net change in valuation allowance ​ (30,568) ​ (25,583) ​ (19,207) Nondeductible expenses ​ (5,041) ​ (4,972) ​ (2,648) Change in fair value of contingent consideration ​ — ​ — ​ 962 Income tax benefit / (expense) ​ $ 16,419 ​ $ — ​ $ (231)
Schedule of significant portions of deferred tax assets and deferred tax liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ ​ 2020 ​ 2019 ​ ​ (in thousands) Deferred tax assets: ​ ​ Net operating loss carryforwards ​ $ 158,614 ​ $ 99,644 Lease liabilities ​ ​ 9,515 ​ ​ 7,861 Intangible assets ​ 1,702 ​ 770 Interest carryforwards ​ ​ 1,597 ​ ​ — Accrued expenses and other current liabilities ​ ​ 1,118 ​ ​ 628 Property, plant and equipment ​ 1,072 ​ 761 Derivative financial instrument ​ ​ 661 ​ ​ - Deferred revenue ​ — ​ 6,676 Gross deferred tax asset ​ $ 174,279 ​ $ 116,340 Less valuation allowance ​ (150,113) ​ (109,856) Net deferred tax asset ​ $ 24,166 ​ $ 6,484 Right-of-use asset ​ ​ (7,702) ​ ​ (6,484) Prepaid expenses ​ ​ (45) ​ ​ — Deferred tax liability ​ $ (7,747) ​ $ (6,484) Net deferred tax asset ​ $ 16,419 ​ $ —
Summary of Changes in the valuation allowance	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 2018 ​ ​ (in thousands) January 1, ​ $ 109,856 ​ $ 85,100 ​ $ 93,682 Changes related to reduction of deferred revenue recorded in equity upon implementation of ASC 606 Revenue recognition as of January 1, 2018 ​ ​ — ​ ​ — ​ ​ (6,229) Changes recorded in profit and loss ​ ​ 30,568 ​ ​ 25,583 ​ ​ 19,207 Increase/(reduction) related to 2020, 2019 and 2018 Dutch tax reforms ​ 18,287 ​ 4,059 ​ (15,670) Release of valuation allowance related to expected current year and future periods recorded in profit and loss ​ ​ (16,419) ​ ​ — ​ ​ — Other changes including currency translation effects ​ 7,821 ​ (4,886) ​ (5,890) December 31, ​ $ 150,113 ​ $ 109,856 ​ $ 85,100
Summary of expiration dates for losses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 2022 2023 2024 2025-2027 ​ ​ (in thousands) Loss expiring ​ $ 15,206 ​ $ 25,878 ​ $ 25,202 ​ $ — ​ $ 521,931

Basic and diluted earnings pe_2

Basic and diluted earnings per share (Tables)	12 Months Ended
	Dec. 31, 2020
Basic and diluted earnings per share
Schedule of potential dilutive common shares	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Years ended December 31, ​ 2020 2019 ​ 2018 ​ ​ (ordinary shares) BMS warrants (derecognized as of December 1, 2020 - see Note 4, "Fair value measurement") ​ — ​ 8,893,000 ​ 8,575,000 Stock options under 2014 Plans ​ 2,659,279 ​ 2,683,104 ​ 2,673,712 Non-vested RSUs and earned PSUs ​ 679,958 ​ 850,252 ​ 789,490 Stock options under previous option plan ​ 14,000 ​ 14,000 ​ 32,567 Hercules warrants (exercised February 1, 2019) ​ — ​ — ​ 37,175 Employee share purchase plan ​ 560 ​ 485 ​ 1,012 Total potential dilutive ordinary shares ​ 3,353,797 ​ 12,440,841 ​ 12,108,956

Summary of significant accoun_4

Summary of significant accounting policies (Details)	12 Months Ended
	Dec. 31, 2020USD ($)segment$ / sharesshares
Segment information
Number of operating segments | segment	1
Earnings Per Common Share
Dilutive securities (in shares) | shares	0
Current and non-current classification
Operating cycle period	12 months
401(k) Plan | Lexington
Pensions
Maximum annual employee contribution as a percent of pre-tax compensation	50.00%
Amount of employer matching contribution for every employee dollar contributed | $	$ 0.50
Lexington | 401(k) Plan
Pensions
Amount contributed to plan (in dollars per share) | $ / shares	$ 1
Maximum | 401(k) Plan | Lexington
Pensions
Percent of employee gross pay for which the employer makes a matching contribution	6.00%
Leasehold improvements | Minimum
Property, plant and equipment, net
Estimated useful life (in years)	10 years
Leasehold improvements | Maximum
Property, plant and equipment, net
Estimated useful life (in years)	15 years
Laboratory equipment
Property, plant and equipment, net
Estimated useful life (in years)	5 years
Office equipment | Minimum
Property, plant and equipment, net
Estimated useful life (in years)	3 years
Office equipment | Maximum
Property, plant and equipment, net
Estimated useful life (in years)	5 years

Collaboration arrangements an_3

Collaboration arrangements and concentration of credit risk - BMS collaboration - Narrative (Details) $ in Thousands	Dec. 17, 2020USD ($)item	Dec. 01, 2020USD ($)item	Jun. 24, 2020USD ($)	May 21, 2015USD ($)	Feb. 28, 2019	Aug. 31, 2015USD ($)	Dec. 31, 2020USD ($)item	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)
Collaboration arrangements
Number of collaboration targets | item							4
License revenues from related party							$ 27,800
Revenue							$ 37,514	$ 7,281	$ 11,284
Tax rate enacted in the Netherlands							25.00%	25.00%	25.00%
CSL Behring collaboration
Collaboration arrangements
Upfront cash to receive upon the closing of the agreement			$ 450,000				$ 450,000
Upfront payment recorded							0
Regulatory and commercial milestone payments received			$ 1,600,000				2,100
CSL Behring collaboration | Transaction Payment Received in 2020
Collaboration arrangements
Upfront cash to receive upon the closing of the agreement							$ 450,000
Tax rate enacted in the Netherlands							25.00%
CSL Behring collaboration | Transaction payment received thereafter
Collaboration arrangements
Upfront cash to receive upon the closing of the agreement							$ 450,000
Other Current Assets | CSL Behring collaboration
Collaboration arrangements
Capitalized Contract Cost, Net							2,100
License revenues from related party
Collaboration arrangements
Revenue							32,967	$ 4,988	$ 7,528
Collaboration revenues from related party
Collaboration arrangements
Revenue							136	2,293	3,756
Collaborative Revenue Including Revenue From Related Party
Collaboration arrangements
Revenue							$ 200	2,300	3,800
BMS arrangement
Collaboration arrangements
Number of collaboration targets | item							4
Revenue							$ 37,514	$ 7,281	11,284
BMS arrangement | Second, Third, and Fourth Targets Selection
Collaboration arrangements
Upfront payment recorded				$ 60,100		$ 15,000
BMS arrangement | Bristol Myers Squibb
Collaboration arrangements
Initial research term							4 years
Number of potential targets included in collaborative agreement | item							10
Extension for research term					1 year
Number of collaboration targets | item	4	4					4	4
Collaboration Agreement, Period From Effective Date Collaboration Targets Can Be Replaced		1 year
Collaboration Agreement, Threshold Number Of Collaboration Targets That Can Be Replaced | item		2
Threshold Number Of New Collaboration Targets In The Field Of Cardiovascular Disease | item		2
Impairment recorded within R&D									5,400
Contingent liability									3,800
Revenue							$ 37,514	$ 7,281	11,284
BMS arrangement | Bristol Myers Squibb | Maximum
Collaboration arrangements
Number of collaboration targets | item		4
License revenue | CSL Behring collaboration
Collaboration arrangements
Revenue							0
License revenue | Bristol Myers Squibb
Collaboration arrangements
Maximum target designation payments to which entitled per agreement							$ (16,500)
Royalty term after the first commercial sale							10 years
Acquired research & development
Collaboration arrangements
Impairment recorded within R&D									$ 5,400
Bristol Myers Squibb | BMS arrangement
Collaboration arrangements
Collaboration Agreement, Threshold Research, Development And Regulatory Milestone Payments Receivable		$ 217,000
Bristol Myers Squibb | Collaborative revenue
Collaboration arrangements
Upfront cash to receive upon the closing of the agreement	$ 4,400
Bristol Myers Squibb | License revenue
Collaboration arrangements
Revenue							$ 4,400

Collaboration arrangements an_4

Collaboration arrangements and concentration of credit risk - Amounts owed by BMS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Number of ordinary shares held	44,777,799	43,711,954
Amounts owed in relation to the collaboration services		$ 947
Total revenues	$ 37,514	7,281	$ 11,284
Bristol Myers Squibb
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Minority interest	5.30%
Bristol Myers Squibb
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Number of ordinary shares held	2,400,000
BMS arrangement
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amounts owed in relation to the collaboration services	$ 4,536	947
Total revenues	37,514	7,281	11,284
BMS arrangement | Bristol Myers Squibb
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amounts owed in relation to the collaboration services	4,536	947
Total revenues	$ 37,514	$ 7,281	$ 11,284

Fair value measurement - Change

Fair value measurement - Changes in Level 3 items (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in Level 3 liabilities
Beginning Balance	$ 3,075	$ 1,375	$ 5,599
Net (gains) losses recognized in profit or loss	(2,300)	2,530	(4,054)
Exercise of Hercules warrants		(770)
Derecognition of warrants	(796)
Currency translation effects	53	(60)	170
Ending Balance	2,645	3,075	1,375
CoC-payment
Changes in Level 3 liabilities
Recognition of derivative financial liability of CoC-payment	2,613
Contingent consideration
Changes in Level 3 liabilities
Beginning Balance			3,964
Net (gains) losses recognized in profit or loss			(3,846)
Currency translation effects			118
Derivative financial instruments
Changes in Level 3 liabilities
Beginning Balance	3,075	1,375	1,635
Net (gains) losses recognized in profit or loss	(2,300)	2,530	(208)
Exercise of Hercules warrants		(770)
Derecognition of warrants	(796)
Currency translation effects	53	(60)	52
Ending Balance	2,645	$ 3,075	$ 1,375
Derivative financial instruments | CoC-payment
Changes in Level 3 liabilities
Recognition of derivative financial liability of CoC-payment	$ 2,613

Fair value measurement - BMS wa

Fair value measurement - BMS warrants - Narrative (Details) $ / shares in Units, $ in Thousands	Dec. 17, 2020item	Dec. 01, 2020USD ($)item	Dec. 31, 2020USD ($)item$ / shares	Dec. 31, 2019USD ($)item	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Apr. 06, 2015$ / shares
Collaboration arrangements
Number of warrant types			2
Number of Collaboration Targets			4
Collaboration Agreement, Cash Payable | $			$ 70,000
Percentage Of Net Proceeds Payable			5
Fair value of derivative financial instruments | $			$ 2,645	$ 3,075	$ 1,375	$ 5,599
Other nonoperating income (expense) | CoC-payment
Collaboration arrangements
Gain (Loss) from the recognition of the derivative financial liability | $			2,600
Non-current liabilities
Collaboration arrangements
Fair value of the derivative financial liability | $		$ 2,600	2,600
Bristol Myers Squibb | Other nonoperating income (expense) | CoC-payment
Collaboration arrangements
Gain (Loss) from the recognition of the derivative financial liability | $			$ (2,600)
BMS arrangement
Collaboration arrangements
Number of Collaboration Targets			4
BMS arrangement | Bristol Myers Squibb
Collaboration arrangements
Number of potential targets included in collaborative agreement			10
Number of Collaboration Targets	4	4	4	4
BMS arrangement | Bristol Myers Squibb | Maximum
Collaboration arrangements
Number of Collaboration Targets		4
BMS Warrants
Collaboration arrangements
Exercise price in respect of each warrant | $ / shares			$ 57.32				$ 33.84
Number of trading days used to calculate Volume Weighted Average Price ("VWAP")			20 days
Number of days prior to purchase or exercise used to calculate Volume Weighted Average Price ("VWAP")			5 days
Compounded annual growth rate used to determine fair value of exercise price			10.00%
BMS Warrants | Bristol Myers Squibb | Other nonoperating income (expense)
Collaboration arrangements
Gain (Loss) from the recognition of the derivative financial liability | $			$ 800
BMS Warrants | BMS arrangement
Collaboration arrangements
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | $			$ 800
BMS Warrants | Recurring
Collaboration arrangements
Derivative Asset | $				$ 3,100
Collaboration Agreement, If 70 Million Is Greater Than Five Percent Of Net Proceeds | Derecognition Of Warrants
Collaboration arrangements
Threshold Percentage Of Net Proceeds			5
Collaboration Agreement, If 70 Million Is Lesser Than One Percent Of Net Proceeds | Derecognition Of Warrants
Collaboration arrangements
Threshold Percentage Of Net Proceeds			1
Percentage Of Net Proceeds Payable			1
Bristol Myers Squibb | uniQure N.V. | First Six New Targets Or Designation Of Sixth Target | BMS Warrants
Collaboration arrangements
Ownership percentage required per agreement			14.90%
Bristol Myers Squibb | uniQure N.V. | First Six New Targets Or Designation Of Sixth Target | BMS Warrants | Minimum
Collaboration arrangements
Number of Collaboration Targets			6
Bristol Myers Squibb | uniQure N.V. | First Six New Targets Or Designation Of Sixth Target | BMS Warrants | Maximum
Collaboration arrangements
Number of Collaboration Targets			7
Bristol Myers Squibb | uniQure N.V. | First Nine New Targets Or Designation Of Ninth Target | BMS Warrants
Collaboration arrangements
Ownership percentage required per agreement			19.90%
Bristol Myers Squibb | uniQure N.V. | First Nine New Targets Or Designation Of Ninth Target | BMS Warrants | Minimum
Collaboration arrangements
Number of Collaboration Targets			9
Bristol Myers Squibb | uniQure N.V. | First Nine New Targets Or Designation Of Ninth Target | BMS Warrants | Maximum
Collaboration arrangements
Number of Collaboration Targets			10

Fair value measurement - Sensit

Fair value measurement - Sensitivity analysis on warrants (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Level 3 | BMS Warrants | Other nonoperating income (expense)
Fair value measurements
Gain (Loss) recorded due to changes in fair value of derivative asset	$ 3.1	$ (2.3)	$ 0.5

Fair value measurement - Hercul

Fair value measurement - Hercules loan facility and Contingent consideration (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 01, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 13, 2019	Sep. 10, 2019	May 07, 2018	Dec. 31, 2017
Fair value measurements
Issue price per share					$ 46	$ 46	$ 28.50
Proceeds from exercise of warrants			$ 500
Net (gains) losses recognized in profit or loss		$ (2,300)	2,530	$ (4,054)
Contingent consideration
Fair value of contingent liability		2,645	3,075	1,375				$ 5,599
Recurring | Level 3 | Hercules Loan Facility Warrant | Other nonoperating income (expense)
Fair value measurements
Net (gains) losses recognized in profit or loss		$ 0	$ (200)	(300)
Bristol Myers Squibb | BMS arrangement | Hercules Warrants
Fair value measurements
Number of shares issued for exercise of warrants	37,175
Issue price per share	$ 34.25
Proceeds from exercise of warrants	$ 500
Contingent consideration
Fair value measurements
Net (gains) losses recognized in profit or loss				(3,846)
Contingent consideration
Fair value of contingent liability								$ 3,964
InoCard | Contingent consideration
Contingent consideration
Change in contingent consideration				$ 3,800

Property, plant and equipment_3

Property, plant and equipment, net - Summary of PP&E (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, plant and equipment, net
Total property, plant, and equipment	$ 67,554	$ 57,396
Less accumulated depreciation	(35,226)	(28,625)
Property, plant and equipment, net	32,328	28,771
Depreciation	5,700	6,000	$ 6,500
Leasehold improvements
Property, plant and equipment, net
Total property, plant, and equipment	37,849	34,611
Laboratory equipment
Property, plant and equipment, net
Total property, plant, and equipment	22,106	18,232
Office equipment
Property, plant and equipment, net
Total property, plant, and equipment	5,025	4,212
Construction-in-progress
Property, plant and equipment, net
Total property, plant, and equipment	$ 2,574	$ 341

Property, plant and equipment_4

Property, plant and equipment, net - PP&E by geographic region (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Long-lived assets
Long-lived assets	$ 32,328	$ 28,771
Lexington
Long-lived assets
Long-lived assets	15,949	15,490
Amsterdam
Long-lived assets
Long-lived assets	$ 16,379	$ 13,281

Right-of-use asset and lease _3

Right-of-use asset and lease liabilities - Narrative (Details) € in Millions, $ in Millions	1 Months Ended		12 Months Ended
	Nov. 30, 2018ft²item	May 31, 2017facility	Dec. 31, 2020USD ($)	Dec. 31, 2020EUR (€)	Dec. 31, 2019	Dec. 31, 2018USD ($)	Dec. 01, 2017	Jun. 30, 2016	Mar. 31, 2016	Nov. 30, 2013
Leases
Area of facility (in square feet) | ft²	30,655
Lease incentives | $						$ 12.2
Weighted-average remaining lease term, Operating leases			9 years 4 months 24 days	9 years 4 months 24 days	10 years 3 months 18 days
Weighted-average discount rate, Operating leases			11.37%	11.37%	11.33%
Lexington
Leases
Lease term (in years)	5 years									10 years
Number of subsequent renewals | item	2
Renewal term (in years)	5 years
Amsterdam
Leases
Lease term (in years)							10 years		16 years
Renewal term (in years)								5 years
Number of facility sites consolidated into new site | facility		3
Minimum rentals to be received			$ 6.6	€ 5.4

Right-of-use asset and lease _4

Right-of-use asset and lease liabilities - Operating lease liabilities (Details) $ in Thousands	Dec. 01, 2017floor	Feb. 29, 2020floor	Dec. 31, 2020USD ($)$ / €	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jan. 01, 2019USD ($)
Components of lease cost
Operating lease cost			$ 5,052	$ 4,474
Variable lease cost			607	507
Sublease income			(904)	(1,053)
Total lease cost			4,755	3,928
Operating Leases, Rent Expense, Net					$ 3,250
Assets
Operating lease right-of-use assets			26,086	26,797
Right-of-use assets in exchange for lease obligations				9,000
Current liabilities
Current operating lease liability			5,524	5,865
Non-current liabilities
Non-current operating lease liability			30,403	31,133
Total lease liabilities			$ 35,927	$ 36,998
Weighted-average remaining lease term, Operating leases			9 years 4 months 24 days	10 years 3 months 18 days
Weighted-average discount rate, Operating leases			11.37%	11.33%
Supplemental cash flow information related to leases
Cash paid for amounts included in the measurement of lease liabilities, Operating cash flows for operating leases			$ 5,769	$ 4,717
Right-of-use asset obtained in exchange for lease obligation
Right-of-use assets in exchange for lease obligations				9,000
Landlord incentive payments				1,500
Undiscounted Cash Flows
2021			5,524
2022			5,621
2023			5,719
2024			6,215
2024			6,534
Thereafter			28,518
Total minimum lease payments			58,131
Less: amount of lease payments representing interest			(22,204)
Total lease liabilities			35,927	36,998
Less: current obligations under operating leases			(5,524)	(5,865)
Non-current operating lease liability			$ 30,403	$ 31,133
Exchange rate (in USD per Euro) | $ / €			1.23
ASU 2016-02
Assets
Operating lease right-of-use assets						$ 19,000
Lexington
Components of lease cost
Operating Leases, Rent Expense, Net					1,583
Current liabilities
Current operating lease liability			$ 3,455
Non-current liabilities
Non-current operating lease liability			19,516
Total lease liabilities			22,971
Undiscounted Cash Flows
2021			3,455
2022			3,552
2023			3,650
2024			4,146
2024			4,465
Thereafter			16,279
Total minimum lease payments			35,547
Less: amount of lease payments representing interest			(12,576)
Total lease liabilities			22,971
Less: current obligations under operating leases			(3,455)
Non-current operating lease liability			19,516
Amsterdam
Components of lease cost
Operating Leases, Rent Expense, Net					$ 1,667
Number of floor of the facility | floor	7
Number of floors to sub-lease | floor	3
Number of floor to take back from the sub-lease | floor		1
Current liabilities
Current operating lease liability			2,069
Non-current liabilities
Non-current operating lease liability			10,887
Total lease liabilities			12,956
Undiscounted Cash Flows
2021			2,069
2022			2,069
2023			2,069
2024			2,069
2024			2,069
Thereafter			12,239
Total minimum lease payments			22,584
Less: amount of lease payments representing interest			(9,628)
Total lease liabilities			12,956
Less: current obligations under operating leases			(2,069)
Non-current operating lease liability			$ 10,887

Intangible assets - Summary of

Intangible assets - Summary of acquired licenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Intangible assets
Intangible assets, net	$ 3,361	$ 5,427
Weighted average remaining life	8 years 6 months
Capitalized expenditures related to milestone payments	$ 2,200	1,000
Licenses
Intangible assets
Total intangible assets	5,660	8,317
Less accumulated amortization	(2,299)	(2,890)
Intangible assets, net	$ 3,361	$ 5,427
Acquired research & development
Intangible assets
Intangible assets, net			$ 0

Intangible assets - Future amor

Intangible assets - Future amortization expense (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Estimated amortization expense for the next five years
Intangible assets, net	$ 3,361	$ 5,427
Licenses
Estimated amortization expense for the next five years
2021	1,277
2022	427
2023	144
2024	144
2025	144
Thereafter	1,225
Intangible assets, net	$ 3,361	$ 5,427

Intangible assets - Carrying am

Intangible assets - Carrying amount of Licenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Intangible assets
Carrying amount	$ 3,361	$ 5,427
Licenses
Intangible assets
Carrying amount	3,361	5,427
Amortization of Intangible Assets	4,600	600	$ 400
Impairment expense related to licenses	$ 300	$ 0	100
Acquired research & development
Intangible assets
Carrying amount			0
Impairment expense related to licenses			$ 5,400

Accrued expenses and other cu_3

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued expenses and other current liabilities
Accruals for services provided by vendors-not yet billed	$ 8,269	$ 5,425
Personnel related accruals and liabilities	7,687	7,032
Contract liability	2,082
Total	$ 18,038	$ 12,457

Long-term debt (Details)

Long-term debt (Details) - USD ($) $ in Thousands	Dec. 06, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 31, 2020
Long-term Debt
Proceeds from loan increment				$ 14,775
Aggregate maturities of loan
Coupon interest payments and financing fees		$ 7,400
2021		3,141
2022		25,002
2023		14,269
Long-term debt		42,412
2016 Amended Facility | Hercules | Second Amended and Restated Loan and Security Agreement [Member]
Long-term Debt
Outstanding debt	$ 20,000
Back-end fees due					$ 1,000
2018 Amended Facility
Long-term Debt
Outstanding debt		35,000
2018 Amended Facility | Hercules
Long-term Debt
Aggregate amount of Equity Financing		90,000
Foreign currency loss			$ 700	900
Foreign currency gain		3,100
2018 Amended Facility | Hercules | Second Amended and Restated Loan and Security Agreement [Member]
Long-term Debt
Outstanding debt	$ 35,000		35,000
Interest rate (as a percent)	8.85%
Back-end fee (as a percent)	4.95%
Borrowing capacity subject to discretion		$ 15,000
Additional unconditional borrowing capacity	$ 15,000
Proceeds from loan increment	$ 15,000
Facility fee (as a percent)	0.50%
2018 Amended Facility | Prime Rate | Hercules | Second Amended and Restated Loan and Security Agreement [Member]
Long-term Debt
Variable interest rate basis	8.85%
Discount rate (as a percent)	5.50%
Venture debt loan facility | 2018 Amended Facility
Long-term Debt
Minimum cash and cash equivalents in U.S. bank accounts		65.00%
Assets pledged to secure facilities by directly or indirectly		$ 340,400
Assets not being pledged to secure facilities by directly or indirectly		115,200
Aggregate maturities of loan
Long-term debt		35,900	36,300
Venture debt loan facility | 2018 Amended Facility | Hercules
Long-term Debt
Interest expense recorded		$ 3,700	$ 3,700	$ 2,000

Shareholders' equity (Details)

Shareholders' equity (Details) € / shares in Units, $ / shares in Units, $ in Thousands, € in Millions	Sep. 13, 2019USD ($)$ / sharesshares	Sep. 10, 2019$ / sharesshares	Feb. 01, 2019USD ($)$ / sharesshares	May 07, 2018USD ($)$ / sharesshares	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2020USD ($)$ / €shares	Dec. 31, 2020EUR (€)€ / shares$ / €shares	Dec. 31, 2019€ / shares	Dec. 31, 2019USD ($)shares
Authorized share capital							$ 3,700	€ 3
Exchange rate (in USD per Euro) | $ / €							1.23	1.23
Shares authorized | shares							60,000,000	60,000,000		60,000,000
Ordinary shares, par value (in euros per share) | € / shares								€ 0.05	€ 0.05
Reserves for foreign currency translation effects						$ 7,300	$ 9,900			$ 6,700
Shares issued in connection with offering | shares	733,695	4,891,305		5,175,000
Offering price per share of shares issued | $ / shares	$ 46	$ 46		$ 28.50
Gross Proceeds From Issuance Initial Public Offering	$ 258,800			$ 147,500
Proceeds from issuance initial public offering					$ 242,718	$ 138,361
Net proceeds from issuance of common stock	242,700
Expenses capitalized related to offering	$ 600			$ 200
Proceeds from exercise of warrants					$ 500
Hercules Warrants | BMS arrangement | Bristol Myers Squibb
Offering price per share of shares issued | $ / shares			$ 34.25
Number of shares issued for exercise of warrants | shares			37,175
Proceeds from exercise of warrants			$ 500

Share-based compensation - Summ

Share-based compensation - Summary of share-based compensation expense and unrecognized costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2015
Share-based compensation
Share-based compensation expense	$ 21,788	$ 17,468	$ 10,693
Unrecognized compensation costs	$ 39,744
Weighted-average remaining period for recognition (in years)	2 years 5 months 12 days
2014 Plan
Share-based compensation
Authorized shares	8,601,471		3,000,000
Increase in authorized shares				3,000,000	1,070,000
Outstanding of fully vested share options	2,659,279	2,683,104
2012 Plan
Share-based compensation
Outstanding of fully vested share options	14,000	14,000
Research and development expenses | Employees
Share-based compensation
Share-based compensation expense	$ 11,965	$ 8,029	$ 3,994
Selling, general and administrative expense | Employees
Share-based compensation
Share-based compensation expense	9,823	9,439	6,699
Share options
Share-based compensation
Share-based compensation expense	11,434	7,896	4,766
Unrecognized compensation costs	$ 23,492
Weighted-average remaining period for recognition (in years)	2 years 9 months 10 days
Restricted share units ("RSUs")
Share-based compensation
Share-based compensation expense	$ 7,364	4,117	3,020
Unrecognized compensation costs	$ 14,489
Weighted-average remaining period for recognition (in years)	2 years 1 month 2 days
Performance share units ("PSUs")
Share-based compensation
Share-based compensation expense	$ 2,990	$ 5,455	$ 2,907
Unrecognized compensation costs	$ 1,763
Weighted-average remaining period for recognition (in years)	1 year 10 days

Share-based compensation - Opti

Share-based compensation - Option activity and weighted-average assumptions (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2015
Weighted-average assumptions used to estimate fair value of share options granted during year
Expected terms (in years)	10 years	10 years	10 years
Risk free interest rate, minimum (as a percent)	0.76%	1.92%	2.67%
Risk free interest rate, maximum (as a percent)	1.44%	2.87%	3.20%
Expected dividend (as a percent)	0.00%	0.00%	0.00%
Minimum
Weighted-average assumptions used to estimate fair value of share options granted during year
Expected volatility (as a percent)	70.00%	70.00%	75.00%
Maximum
Weighted-average assumptions used to estimate fair value of share options granted during year
Expected volatility (as a percent)		75.00%	80.00%
Share options
Weighted average remaining contractual life (in years)
Exercised (in dollars)	$ 11,927	$ 17,700	$ 7,515
Aggregate intrinsic value
Exercised (in dollars)	$ 11,927	$ 17,700	$ 7,515
2014 Plan
Options
Outstanding at beginning of year (in shares)	2,683,104
Granted (in shares)	653,852
Forfeited (in shares)	(172,548)
Expired (in shares)	(6,451)
Exercised (in shares)	(498,678)	(434,665)	(388,203)
Outstanding at end of year (in shares)	2,659,279	2,683,104
Thereof, fully vested and exercisable at end of period (in shares)	1,542,405
Thereof, outstanding and expected to vest at end of period (in shares)	1,116,874	1,346,337
Weighted average exercise price
Outstanding at beginning of year (in dollars per share)	$ 21.29
Granted (in dollars per share)	49.63
Forfeited (in dollars per share)	42.03
Expired (in dollars per share)	45.76
Exercised (in dollars per share)	14.43
Outstanding at end of year (in dollars per share)	28.13	$ 21.29
Thereof, fully vested and exercisable at end of year (in dollars per share)	18.05
Outstanding and expected to vest at end of year (in dollars per share)	$ 42.06	$ 28.76
Total weighted average grant date fair value of options issued during the period (in $ millions)	$ 18,400
Proceeds from option sales during the period (in $ millions)	$ 7,200
Vesting period (in years)	4 years
Weighted-average assumptions used to estimate fair value of share options granted during year
Increase in authorized shares				3,000,000	1,070,000
Weighted average remaining contractual life (in years)
Outstanding	7 years 2 months 4 days	7 years 5 months 15 days
Thereof, fully vested and exercisable at end of year	6 years 1 month 24 days
Outstanding and expected to vest at end of year	8 years 7 months 9 days
Aggregate intrinsic value
Outstanding (in dollars)	$ 32,729	$ 135,238
Thereof, fully vested and exercisable	29,161
Outstanding and expected to vest	$ 3,568
2014 Plan | Share options
Options
Granted (in shares)	653,852	647,526	937,832
Forfeited (in shares)	(172,548)
Thereof, outstanding and expected to vest at end of period (in shares)	1,116,874	1,346,337
Weighted average exercise price
Outstanding and expected to vest at end of year (in dollars per share)	$ 24.25	$ 17.05
Weighted average grant-date fair value
Vested (in shares)	713,924
Vested (in dollar per share)	$ 14.04
Forfeited (in dollar per share)	$ 24.63
2014 Plan | Non-executive directors
Weighted average exercise price
Vesting period (in years)	1 year
2014 Plan | Directors and Officers
Options
Granted (in shares)	209,254
Weighted average exercise price
Granted (in dollars per share)	$ 5.7
2014 Plan | One year from grant date
Weighted average exercise price
Vesting percentage per year	25.00%
Vesting period (in years)	1 year

Share-based compensation - RSU

Share-based compensation - RSU activity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
2014 Plan
Other disclosure
Vesting period (in years)		4 years
2014 Plan | Non-executive directors
Other disclosure
Vesting period (in years)		1 year
Restricted share units ("RSUs")
Number of shares
Non-vested at beginning of year (in shares)		370,830
Restricted stock granted (in shares)		376,799
Vested (in shares)		(206,881)
Forfeited (in shares)		(73,404)
Non-vested at end of year (in shares)		467,344	370,830
Weighted average grant-date fair value
Non-vested at beginning of year (in dollars per share)		$ 28.62
Granted (in dollars per share)		48.18
Vested (in dollars per share)		24.18
Forfeited (in dollars per share)		46.41
Non-vested at end of year (in dollars per share)		$ 43.56	$ 28.62
Other disclosure
Total weighted average grant date fair value of RSUs granted during the period (in millions)		$ 18,200
Restricted share units ("RSUs") | Non-executive directors
Other disclosure
Vesting period (in years)	1 year
Restricted share units ("RSUs") | Directors and Officers
Number of shares
Restricted stock granted (in shares)		158,623
Weighted average grant-date fair value
Granted (in dollars per share)		$ 7.4
Restricted share units ("RSUs") | 2014 Plan
Number of shares
Restricted stock granted (in shares)		376,799	198,504	262,599
Weighted average grant-date fair value
Granted (in dollars per share)		$ 48.18	$ 38.63	$ 23.61
Other disclosure
Total weighted average grant date fair value of RSUs granted during the period (in millions)		$ 12,156	$ 10,152	$ 8,546
Share options | 2014 Plan
Weighted average grant-date fair value
Granted (in dollars per share)		$ 28.08	$ 23.57	$ 15.90
Minimum | Restricted share units ("RSUs")
Other disclosure
Vesting period (in years)		1 year
Maximum | Restricted share units ("RSUs")
Other disclosure
Vesting period (in years)		3 years

Share-based compensation - PSU

Share-based compensation - PSU activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
2014 Plan
Other disclosure
Vesting period (in years)	4 years
Performance share units ("PSUs")
Number of shares
Non-vested at beginning of year (in shares)	479,422
Restricted stock granted (in shares)	91,003
Vested (in shares)	(354,105)
Forfeited (in shares)	(3,706)
Non-vested at end of year (in shares)	212,614	479,422
Weighted average grant-date fair value
Non-vested at beginning of year (in dollars per share)	$ 21.17
Granted (in dollars per share)	57.56
Vested (in dollars per share)	17.44
Forfeited (in dollars per share)	57.56
Non-vested at end of year (in dollars per share)	$ 42.32	$ 21.17
Other disclosure
Total weighted average grant date fair value of RSUs granted during the period (in millions)	$ 5,200
Performance share units ("PSUs") | 2014 Plan
Number of shares
Restricted stock granted (in shares)	91,003	132,362
Weighted average grant-date fair value
Granted (in dollars per share)	$ 57.56	$ 31.71
Other disclosure
Total weighted average grant date fair value of RSUs granted during the period (in millions)	$ 21,852	$ 1,056	$ 1,350
Share options | 2014 Plan
Weighted average grant-date fair value
Granted (in dollars per share)	$ 28.08	$ 23.57	$ 15.90

Share-based compensation - Empl

Share-based compensation - Employee Share Purchase Plan - Narrative (Details) - ESPP - Employee Stock [Member] - shares	1 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based compensation
Ordinary shares available for issue	150,000	132,026
Discounted rate for purchase of shares	85.00%
Number of shares issued		6,181	9,202	2,591

Expenses by nature - Operating

Expenses by nature - Operating expenses excluding expenses presented in other expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Employee-related expenses	$ 75,926	$ 59,130	$ 46,254
Laboratory and development expenses	35,977	30,130	23,596
Office and housing expenses	13,388	10,588	7,281
Legal and advisory expenses	17,370	11,297	7,748
Depreciation, amortization and impairment expenses	10,648	6,669	12,415
Patent and license expenses	2,899	1,654	1,202
Other operating expenses	8,772	8,813	1,618
Total	$ 164,980	$ 128,281	$ 100,114

Expenses by nature - Employee-r

Expenses by nature - Employee-related expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee-related expenses
Wages and salaries	$ 40,919	$ 32,029	$ 26,646
Share-based compensation expenses	21,831	17,533	10,708
Consultant expenses	2,423	2,464	2,974
Social security costs	4,068	2,727	2,231
Health insurance	2,271	1,933	1,471
Pension costs - defined contribution plans	1,779	1,052	907
Other employee expenses	2,635	1,392	1,317
Total	$ 75,926	$ 59,130	$ 46,254

Other non-operating income _ _3

Other non-operating income / (expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other non-operating income
Derivative gains	$ 483		$ 208
Total other non-operating income:	483		208
Other non-operating expense
Derivative losses		$ (2,530)
Total other non-operating expense:		(2,530)
Other non-operating income / (expense), net	483	(2,530)	208
Gain (Loss) recorded due to changes in fair value of derivative liability	(2,300)	2,530	(4,054)
CoC-payment | Other nonoperating income (expense)
Other non-operating expense
Gain (Loss) from the recognition of the derivative financial liability	2,600
Recurring | Level 3 | BMS Warrants | Other nonoperating income (expense)
Other non-operating expense
Gain (Loss) recorded due to changes in fair value of derivative liability	2,300
Recurring | Level 3 | Hercules Loan Facility Warrant | Other nonoperating income (expense)
Other non-operating expense
Gain (Loss) recorded due to changes in fair value of derivative liability	0	(200)	(300)
Bristol Myers Squibb
Other non-operating income
Derivative gains	500		$ 500
Other non-operating expense
Derivative losses		$ 2,300
Bristol Myers Squibb | BMS Warrants | Other nonoperating income (expense)
Other non-operating expense
Gain (Loss) from the recognition of the derivative financial liability	800
Bristol Myers Squibb | CoC-payment | Other nonoperating income (expense)
Other non-operating expense
Gain (Loss) from the recognition of the derivative financial liability	$ (2,600)

Income taxes - Loss before inco

Income taxes - Loss before income taxes and income tax benefit / (expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss before income taxes
Unrecognized Tax Benefits	$ 0	$ 0
Dutch operations	(130,493)	(111,820)	$ (85,721)
Loss before income tax income / (expense)	(141,443)	(124,201)	(83,073)
Current tax expense
Dutch operations	0
Total current tax expense			(22)
Deferred tax benefit / (expense)
Dutch operations			(209)
Total deferred tax benefit / (expense)	16,419		(209)
Income tax benefit / (expense)	16,419		(231)
U.S. operations
Loss before income taxes
Loss before income tax benefit / (expense)	(10,950)	$ (12,381)	2,646
Current tax expense
Current benefit / (expense)	0
Deferred tax benefit / (expense)
Deferred benefit / (expense)	$ 16,419
Foreign operations
Loss before income taxes
Loss before income tax benefit / (expense)			3
Current tax expense
Current benefit / (expense)			$ (22)

Income taxes - Tax rate reconci

Income taxes - Tax rate reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Tax rate reconciliation
Loss before income tax income / (expense) for the period	$ (141,443)	$ (124,201)	$ (83,073)
Expected income tax benefit at the tax rate enacted in the Netherlands (25%)	35,361	31,050	20,768
Difference in tax rates between the Netherlands and the U.S. as well as other foreign countries	247	(495)	(106)
Release of valuation allowance related to expected future taxable income	(30,568)	(25,583)	(19,207)
Other net change in valuation allowance	(30,568)	(25,583)	(19,207)
Nondeductible expenses	(5,041)	$ (4,972)	(2,648)
Change in fair value of contingent consideration			962
Income tax benefit / (expense)	$ 16,419		$ (231)
Tax rate enacted in the Netherlands	25.00%	25.00%	25.00%
Non-deductible expenses, Share-based compensation	$ 5,800	$ 4,400	$ 2,700
Non-deductible expenses, Derivatives	800	$ 600	$ 0
U.S. operations
Tax rate reconciliation
Release of valuation allowance related to expected future taxable income	$ 16,419
Tax rate enacted in the Netherlands	21.00%

Income taxes - Significant comp

Income taxes - Significant components of deferred taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 158,614	$ 99,644
Lease liabilities	9,515	7,861
Intangible assets	1,702	770
Interest carryforwards	1,597
Accrued expenses and other current liabilities	1,118	628
Property, plant and equipment	1,072	761
Derivative financial instrument	661
Deferred revenue		6,676
Gross deferred tax asset	174,279	116,340
Less valuation allowance	150,113	109,856	$ 85,100	$ 93,682
Net deferred tax asset	24,166	6,484
Deferred tax liabilities:
Right-of-use asset	(7,702)	(6,484)
Prepaid expenses	(45)
Net deferred tax liability	(7,747)	$ (6,484)
Net deferred tax asset	$ 16,419

Income taxes - Changes in valua

Income taxes - Changes in valuation allowance (Details) - USD ($) $ in Thousands	Jun. 24, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Opening balance		$ 109,856	$ 85,100	$ 93,682
Changes related to reduction of deferred revenue recorded in equity upon implementation of ASC 606 Revenue recognition as of January 1, 2018				(6,229)
Changes recorded in profit and loss		30,568	25,583	19,207
Increase/(reduction) related to 2020, 2019 and 2018 Dutch tax reforms		18,287	4,059	(15,670)
Other changes including currency translation effects		7,821	(4,886)	(5,890)
Ending balance		150,113	109,856	$ 85,100
Amount of valuation allowance for deferred tax assets within contributed capital as it relates to follow on offering costs.		$ 7,700	$ 6,900
Tax rate enacted in the Netherlands		25.00%	25.00%	25.00%
U.S. operations
Changes recorded in profit and loss		$ (16,419)
Release of valuation allowance related to expected current year and future periods recorded in profit and loss		$ (16,419)
Tax rate enacted in the Netherlands		21.00%
CSL Behring collaboration
Upfront cash to receive upon the closing of the agreement	$ 450,000	$ 450,000
Transaction Payment Received in 2020 | CSL Behring collaboration
Upfront cash to receive upon the closing of the agreement		$ 450,000
Tax rate enacted in the Netherlands		25.00%
Transaction payment received thereafter | CSL Behring collaboration
Upfront cash to receive upon the closing of the agreement		$ 450,000

Income taxes - Effective Tax Ra

Income taxes - Effective Tax Rate (Details) - USD ($) $ in Millions	Jan. 01, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net operating loss carryforwards utilization			$ 1.2	$ 0.8	$ 0.9
U.S. corporate statutory income tax rate (as a percent)			25.00%	25.00%	25.00%
Operating loss carryforwards period (in years)	6 years		9 years
Forecast | Maximum
U.S. corporate statutory income tax rate (as a percent)		25.00%
U.S. operations
U.S. corporate statutory income tax rate (as a percent)			21.00%
Effective income tax rate			27.32%

Income taxes - Tax losses expir

Income taxes - Tax losses expiring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Tax loss carry-forwards
Tax loss carry-forwards	$ 588,200	$ 414,000	$ 311,700
Valuation allowances	$ 16,400
Maximum
Tax loss carry-forwards
Tax loss carry-forward expiration (in years)	7 years
Minimum
Tax loss carry-forwards
Tax loss carry-forward expiration (in years)	6 years
2019
Tax loss carry-forwards
Loss expiring		$ 20,700
2020
Tax loss carry-forwards
Loss expiring	$ 18,500
2021
Tax loss carry-forwards
Loss expiring	15,206
2022
Tax loss carry-forwards
Loss expiring	25,878
2023
Tax loss carry-forwards
Loss expiring	25,202
Tax Year 2025 To 2028 [Member]
Tax loss carry-forwards
Loss expiring	521,931
U.S. operations | 2020
Tax loss carry-forwards
Tax loss carry-forwards	$ 42,300

Basic and diluted earnings pe_3

Basic and diluted earnings per share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic and diluted earnings per share
Total potential dilutive ordinary shares	3,353,797	12,440,841	12,108,956
BMS Warrants
Basic and diluted earnings per share
Total potential dilutive ordinary shares		8,893,000	8,575,000
Stock options | 2014 Plan
Basic and diluted earnings per share
Total potential dilutive ordinary shares	2,659,279	2,683,104	2,673,712
Stock options | Previous option plan
Basic and diluted earnings per share
Total potential dilutive ordinary shares	14,000	14,000	32,567
Stock options | ESPP
Basic and diluted earnings per share
Total potential dilutive ordinary shares	560	485	1,012
Non-vested and earned RSUs and PSUs
Basic and diluted earnings per share
Total potential dilutive ordinary shares	679,958	850,252	789,490
Hercules Warrants
Basic and diluted earnings per share
Total potential dilutive ordinary shares			37,175

Related party transaction (Deta

Related party transaction (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Number of ordinary shares held	44,777,799	43,711,954
Bristol Myers Squibb
Related Party Transaction [Line Items]
Minority interest	5.30%
Bristol Myers Squibb
Related Party Transaction [Line Items]
Number of ordinary shares held	2,400,000

Subsequent events (Details)

Subsequent events (Details) - USD ($) $ in Millions	Jan. 31, 2021	Jan. 29, 2021	Jan. 31, 2021	Dec. 15, 2021	Dec. 31, 2020
2018 Amended Facility
Subsequent events
Outstanding debt					$ 35
2021 Amended Facility
Subsequent events
Maximum borrowing capacity					$ 35
Subsequent events. | 2021 Amended Facility
Subsequent events
Outstanding debt		$ 35		$ 65
Maximum borrowing capacity		135
Interest rate (as a percent)	0.0825%		0.0825%
Facility fees		$ 0.4
Subsequent events. | 2021 Amended Facility | Minimum
Subsequent events
Outstanding debt				$ 20
Back-end fee (as a percent)			1.65%
Subsequent events. | 2021 Amended Facility | Maximum
Subsequent events
Interest rate (as a percent)	825.00%		825.00%
Back-end fee (as a percent)			6.85%
Subsequent events. | 2021 Amended Facility | Prime Rate
Subsequent events
Variable interest rate basis	0.0325%