argenx SE (ARGX) 20-F 31 Mar 20 2019 FY Annual report (foreign) Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2019shares
Cover [Abstract]
Document Type	20-F
Document Registration Statement	false
Document Annual Report	true
Document Transition Report	false
Document Shell Company Report	false
Document Period End Date	Dec. 31, 2019
Entity Registrant Name	ARGENX SE
Entity Common Stock, Shares Outstanding	42,761,528
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Central Index Key	0001697862
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false

CONSOLIDATED STATEMENTS OF FINA

CONSOLIDATED STATEMENTS OF FINANCIAL POSITION - EUR (€) € in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	€ 331,282	€ 281,040	€ 190,867
Restricted cash — current		1,692	1,692
Research and development incentive receivables — current	261	301	158
Financial assets — current	1,004,539	283,529	168,907
Prepaid expenses	9,022	2,995	2,338
Trade and other receivables	28,115	2,886	2,842
Total current assets	1,373,219	572,443	366,804
Non-current assets
Restricted cash — non-current	630	251	256
Research and development incentive receivables — non-current	8,566	4,883	3,033
Other non-current assets			125
Financial assets — non-current	2,596	1	1
Property, plant and equipment	8,167	824	676
Intangible assets	40,161	56	13
Total non-current assets	60,120	6,015	4,104
TOTAL ASSETS	1,433,339	578,458	370,908
Equity
Share capital	4,276	3,597	3,217
Share premium	1,308,539	673,454	430,518
Accumulated losses	(332,568)	(169,603)	(100,568)
Other reserves	70,499	30,947	11,764
Total equity	1,050,746	538,395	344,931
Non-current liabilities	222,636	7	1,460
Provisions for employee benefits	64	7	25
Lease liabilities — non-current	4,540
Deferred revenue — non-current	218,032		1,435
Current liabilities	159,957	40,056	24,517
Lease liabilities — current	1,974
Trade and other payables	85,301	37,072	15,285
Tax liabilities	344	823	597
Deferred revenue - current	72,338	2,161	8,635
Total liabilities	382,593	40,063	25,977
TOTAL EQUITY AND LIABILITIES	€ 1,433,339	€ 578,458	€ 370,908

CONSOLIDATED STATEMENTS OF PROF

CONSOLIDATED STATEMENTS OF PROFIT AND LOSS AND OTHER COMPREHENSIVE INCOME - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CONSOLIDATED STATEMENTS OF PROFIT AND LOSS AND OTHER COMPREHENSIVE INCOME
Revenue	€ 69,783	€ 21,482	€ 36,415
Other operating income	12,801	7,749	4,841
Total operating income	82,584	29,231	41,256
Research and development expenses	(197,665)	(83,609)	(51,740)
Selling, general and administrative expenses	(64,569)	(27,471)	(12,448)
Change in fair value on financials assets	1,096
Operating loss	(178,554)	(81,849)	(22,932)
Financial income	14,399	3,694	1,250
Financial expense	(124)
Exchange gains/(losses)	6,066	12,308	(5,797)
Loss before taxes	(158,213)	(65,847)	(27,479)
Income tax expense	(4,752)	(794)	(597)
Loss for the year and total comprehensive loss	(162,965)	(66,641)	(28,076)
Loss for the year and total comprehensive loss attributable to owners of the parent	€ (162,965)	€ (66,641)	€ (28,076)
Weighted average number of shares outstanding	38,619,121	33,419,356	24,609,536
Basic and diluted loss per share	€ (4.22)	€ (1.99)	€ (1.14)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS (USED IN) / FROM OPERATING ACTIVITIES
Operating result	€ (178,554)	€ (81,849)	€ (22,932)
Adjustments for non-cash items
Amortization of intangible assets	38	19	10
Depreciation of property, plant and equipment	2,128	474	425
Loss on disposal of fixed assets			11
Provisions for employee benefits	57	(18)	24
Expense recognized in respect of share-based payments	39,552	19,183	4,268
Fair value gains on financial assets at fair value through profit or loss	(1,096)
Adjustments for non-cash items	(137,875)	(62,191)	(18,195)
Movements in current assets/liabilities
(Increase)/decrease in trade and other receivables	(22,965)	(44)	(122)
(Increase)/decrease in other current assets	(5,170)	(800)	(1,093)
Increase/(decrease) in trade and other payables	47,995	21,784	3,094
Increase/(decrease) in deferred revenue — current	62,106	(8,868)	(11,501)
Movements in non-current assets/liabilities
(Increase)/decrease in other non‑current assets	(5,560)	(1,720)	(94)
(Increase)/decrease in deferred revenue – non-current	200,533	(1,435)	(8,635)
Cash flows (used in)/from operating activities	139,064	(53,274)	(36,546)
Interest paid	(124)
Income taxes paid	(4,356)	(565)
NET CASH FLOWS (USED IN) / FROM OPERATING ACTIVITIES	134,584	(53,839)	(36,546)
CASH FLOWS (USED IN) / FROM INVESTING ACTIVITIES
Purchase of intangible assets	(40,143)	(62)	(6)
Purchase of property, plant and equipment	(1,604)	(622)	(345)
(Increase)/decrease in financial assets — current	(708,060)	(108,229)	(162,076)
Interest received	5,469	1,371	375
NET CASH FLOWS (USED IN) / FROM INVESTING ACTIVITIES	(744,338)	(107,542)	(162,052)
CASH FLOWS (USED IN) / FROM FINANCING ACTIVITIES
Principal elements of lease payments	(1,353)
Proceeds from issue of new shares, gross amount	678,936	255,721	327,700
Issue costs paid	(22,999)	(14,655)	(23,015)
Exchange gain from currency conversion on proceeds from issue of new shares		1,354
Proceeds from exercise of stock options	4,775	2,251	679
NET CASH FLOWS (USED IN) / FROM FINANCING ACTIVITIES	659,359	244,671	305,365
NET INCREASE (DECREASE) IN CASH & CASH EQUIVALENTS	49,605	83,290	106,767
Cash and cash equivalents at the beginning of the period	281,040	190,867	89,897
Exchange gains/(losses) on cash & cash equivalents	637	6,883	(5,797)
Cash and cash equivalents at the end of the period	€ 331,282	€ 281,040	€ 190,867

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - EUR (€) € in Thousands	Share capital	Share premium	Accumulated losses	Other reserves	Total equity attributable to owners of the parent	Total
Equity at beginning of period at Dec. 31, 2016	€ 2,012	€ 126,358	€ (72,492)	€ 7,496	€ 63,374	€ 63,374
Total comprehensive loss of the period			(28,076)		(28,076)	(28,076)
Share-based payment				4,268	4,268	4,268
Issue of new shares	1,185	326,515			327,700	327,700
Transaction costs for equity issue (restated)		(23,015)			(23,015)	(23,015)
Exercise of stock options	19	660			679	679
Equity at end of period at Dec. 31, 2017	3,216	430,518	(100,568)	11,764	344,931	344,931
Total comprehensive loss of the period						(66,641)
Equity at end of period at Dec. 31, 2018	3,597	673,454	(169,603)	30,947	538,395	538,395
Equity at beginning of period at Jan. 01, 2018	3,216	430,518	(102,962)	11,764	342,536	342,536
Total comprehensive loss of the period			(66,641)		(66,641)	(66,641)
Share-based payment				19,183	19,183	19,183
Issue of new shares	347	255,374			255,721	255,721
Transaction costs for equity issue (restated)		(14,655)			(14,655)	(14,655)
Exercise of stock options	34	2,217			2,251	2,251
Equity at end of period at Dec. 31, 2018	3,597	673,454	(169,603)	30,947	538,395	538,395
Adoption of IFRS 15 (modified retrospective approach)			(2,395)		(2,395)	(2,395)
Total comprehensive loss of the period			(162,965)		(162,965)	(162,965)
Share-based payment				39,552	39,552	39,552
Issue of new shares	637	678,299			678,936	678,936
Transaction costs for equity issue (restated)		(22,999)			(22,999)	(22,999)
Accounting treatment of the share subscription agreement		(24,948)			(24,948)	(24,948)
Exercise of stock options	42	4,733			4,775	4,775
Equity at end of period at Dec. 31, 2019	€ 4,276	€ 1,308,539	€ (332,568)	€ 70,499	€ 1,050,746	€ 1,050,746

General information about the c

General information about the company	12 Months Ended
	Dec. 31, 2019
General information about the company
General information about the company	1. General information about the company argenx SE is a Dutch European public company with limited liability incorporated under the laws of the Netherlands. The company (COC 24435214) has its official seat in Rotterdam, the Netherlands, and its registered office is at Willemstraat 5, 4811 AH, Breda, the Netherlands. An overview of the company and its subsidiaries (the Company) are described in note 32. argenx SE is a publicly traded company with ordinary shares listed on Euronext Brussels under the symbol “ARGX” since July 2014 and with American Depositary Shares listed on Nasdaq under the symbol “ARGX” since May 2017.

Significant accounting policies

Significant accounting policies	12 Months Ended
	Dec. 31, 2019
Significant accounting policies
Significant accounting policies	2. Significant accounting policies The significant Company’s accounting policies are summarized below. 2.1 Statement of compliance and basis of preparation The consolidated financial statements are prepared in accordance with the International Financial Reporting Standards (IFRS), issued by the International Accounting Standards Board (IASB) and the interpretations issued by the IASB’s International Financial Reporting Interpretation Committee. The consolidated financial statements provide a general overview of the Company’s activities and the results achieved. They present fairly the entity’s financial position, its financial performance and cash flows, on a going concern basis. The accounting policies described in Note 2 to our consolidated financial statements have been applied in preparing the consolidated financial statements as of and for the year ended December 31, 2019 and for the comparative information as of and for the years ended December 31, 2018 and 2017. The preparation of consolidated financial statements in conformity with IFRS, issued by the IASB, requires the use of certain critical accounting estimates. It also requires management to exercise its judgment in the process of applying the Company’s accounting policies. The areas involving a higher degree of judgment or complexity, or areas where assumptions and estimates are significant to the consolidated financial statements are disclosed in Note 3. The significant accounting policies applied in the preparation of the above consolidated financial statements are set out below. All amounts are presented in thousands of euro, unless otherwise indicated, rounded to the nearest € ‘000. The consolidated financial statements have been approved for issue by the Company’s Board of Directors (the Board) on March 31, 2020. 2.2 Basis of consolidation The consolidated financial statements include the financial statements of the Company and entities controlled by the Company (its subsidiaries). Control is achieved when the Company: · has power over the investee; · is exposed, or has rights, to variable returns from its involvement with the investee; and · has the ability to use its power to affect its returns. The Company reassesses whether or not it controls an investee if facts and circumstances indicate that there are changes to one or more of the three elements of control listed above. Consolidation of a subsidiary begins when the Company obtains control over the subsidiary and ceases when the Company loses control of the subsidiary. Income and expenses of subsidiaries acquired or disposed of during the year are included in the consolidated statement of profit and loss and other comprehensive income from the effective date of acquisition and up to the effective date of disposal, as appropriate. When necessary, adjustments are made to the financial statements of subsidiaries to bring their accounting policies into line with those used by other members of the Group. All inter-company transactions and unrealized gains on transactions between group companies are eliminated. Unrealised losses are also eliminated unless the transaction provides evidence of an impairment of the transferred asset. Accounting policies of subsidiaries have been changed where necessary to ensure consistency with the policies adopted by the Group. 2.3 Foreign currency transactions Functional and presentation currency The consolidated financial statements are presented in euro (€), which is the Company’s presentation currency and the Company’s functional currency. Transactions and balances Transactions in foreign currencies are translated at the exchange rate ruling at the date of the transaction. Monetary assets and liabilities denominated in foreign currencies are translated at the exchange rate ruling at the reporting date. Foreign exchange differences arising on translation are recognized in the statement of profit and loss and other comprehensive income. Non‑monetary assets and liabilities denominated in foreign currencies are translated at the foreign exchange rate ruling at the date of the transaction. Financial statements of foreign entities For foreign entities using a different functional currency than the euro: · assets and liabilities for each balance sheet presented are translated at the closing rate at the date of that statement of financial position. · income and expenses for each statement presenting profit or loss and other comprehensive income are translated at average exchange rates (unless this average is not a reasonable approximation of the cumulative effect of the rates prevailing on the transaction dates, in which case income and expenses are translated at the rate on the dates of the transactions). · all resulting exchange differences are recognised in other comprehensive income. 2.4 Intangible assets 2.4.1 Internally generated intangible assets Expenditure on research activities is recognized as an expense in the period in which it is incurred. An internally‑generated intangible asset arising from development (or from the development phase of an internal project) is recognized if, and only if, all of the following have been demonstrated: · the technical feasibility of completing the intangible asset so that it will be available for use or sale; · the intention to complete the intangible asset and use or sell it; · the ability to use or sell the intangible asset; · how the intangible asset will generate probable future economic benefits; · the availability of adequate technical, financial and other resources to complete the development and to use or sell the intangible asset; and · the ability to measure reliably the expenditure attributable to the intangible asset during its development. The amount initially recognized for internally‑generated intangible assets is the sum of the expenditure incurred from the date when the intangible asset first meets the recognition criteria listed above. Where no internally‑generated intangible asset can be recognized, development expenditures are recognized in the statement of profit and loss and other comprehensive income in the period in which they are incurred. Due to uncertainties inherent to the development and registration with the relevant healthcare authorities of its products, the Company estimates that the conditions for capitalization are not met until the regulatory procedures required by such healthcare authorities have been finalized. The Company currently does not own products that have been approved by the relevant healthcare authorities. Subsequent to initial recognition, internally‑generated intangible assets are reported at cost less accumulated amortization and accumulated impairment losses, on the same basis as intangible assets that are acquired separately. 2.4.2 Intangible assets acquired separately Intangible assets with finite useful lives that are acquired separately are carried at cost less accumulated amortization and accumulated impairment losses. Amortization is recognized on a straight‑line basis over their estimated useful lives which are disclosed in note 4. The estimated useful life and amortization method are reviewed at the end of each reporting period, with the effect of any changes in estimate being accounted for on a prospective basis. Intangible assets with indefinite useful lives that are acquired separately are carried at cost less accumulated impairment losses. Payments for acquired in-process research and development projects obtained through in-licensing arrangements, business combinations and separate asset purchases are capitalized as intangible assets provided that they are separately identifiable, controlled by the Company and expected to provide future economic benefits. As the probability criterion in IAS 38 is always considered to be satisfied for separately acquired research and development assets and the amount of the payments is determinable, upfront and milestone payments to third parties for pharmaceutical products or compounds for which regulatory marketing approval has not yet been obtained are recognized as intangible assets, and amortized on a straight line basis over their useful lives beginning when the underlying drug candidate is approved and launched commercially, or expensed immediately if development of the drug candidate is abandoned. 2.4.3 Derecognition of intangible assets An intangible asset is derecognized either on disposal or when no future economic benefits are expected from its use. Gains or losses arising from derecognition of an intangible asset, measured as the difference between the net disposal proceeds and the carrying amount of the asset, are recognized in profit or loss when the asset is derecognized. 2.5 Property, plant and equipment Items of property, plant and equipment held for use in the production or supply of goods or services, or for administrative purposes, are stated in the statement of financial position at their cost, less accumulated depreciation and accumulated impairment losses. The cost comprises the initial purchase price plus other direct purchase costs (such as non‑refundable tax and transport). Depreciation is recognized as from acquisition date onwards (unless asset is not ready for use) so as to write off the cost or valuation of assets (other than freehold land and properties under construction) less their residual values over their useful lives, using the straight‑line method. The estimated useful lives, residual values and depreciation method are reviewed at the end of each reporting period, with the effect of any changes in estimate accounted for on a prospective basis. Unless revised due to specific changes in the estimated useful life, annual depreciation rates are as follows: · Office and lab equipment: 3–5 years · IT equipment: 3 years An item of property, plant and equipment is derecognized upon disposal or when no future economic benefits are expected to arise from the continued use of the asset. Any gain or loss arising on the disposal or retirement of an item of property, plant and equipment is determined as the difference between the sales proceeds and the carrying amount of the asset and is recognized in profit or loss. 2.6 Leases As explained in note 2.22 below, the Company has changed its accounting policy for leases where the Company is the lessee. Until December 31, 2018, leases of property, plant and equipment where the Company, as lessee, had substantially all the risks and rewards of ownership were classified as finance leases. Finance leases were capitalised at the lease’s inception at the fair value of the leased property or, if lower, the present value of the minimum lease payments. The corresponding rental obligations, net of finance charges, were included in other short-term and long-term payables. Each lease payment was allocated between the liability and finance cost. The finance cost was charged to the profit or loss over the lease period so as to produce a constant periodic rate of interest on the remaining balance of the liability for each period. The property, plant and equipment acquired under finance leases was depreciated over the asset’s useful life or over the shorter of the asset’s useful life and the lease term if there is no reasonable certainty that the Company will obtain ownership at the end of the lease term. Leases in which a significant portion of the risks and rewards of ownership were not transferred to the Company as lessee were classified as operating leases. Operating lease payments were recognized as an expense on a straight‑line basis over the lease term, except where another systematic basis was more representative of the time pattern in which economic benefits from the leased asset are consumed. As from January 1, 2019, the Company assesses whether a contract is or contains a lease, at inception of the contract. The Company recognises a right-of-use asset and a corresponding lease liability with respect to all lease arrangements in which it is the lessee, except for short-term leases (defined as leases with a lease term of 12 months or less) and leases of low value assets. For these leases, the Company recognises the lease payments as an operating expense on a straight-line basis over the term of the lease unless another systematic basis is more representative of the time pattern in which economic benefits from the leased assets are consumed. The lease liability is initially measured at the present value of the lease payments that are not paid at the commencement date, discounted by using the rate implicit in the lease. If this rate cannot be readily determined, the lessee uses its incremental borrowing rate. The lease liability is subsequently measured by increasing the carrying amount to reflect interest on the lease liability (using the effective interest method) and by reducing the carrying amount to reflect the lease payments made. The lease liability is presented as a separate line in the consolidated statement of financial position. The right-of-use assets comprise the initial measurement of the corresponding lease liability, lease payments made at or before the commencement day, less any lease incentives received and any initial direct costs. They are subsequently measured at cost less accumulated depreciation and impairment losses. Right-of-use assets are depreciated over the shorter period of lease term and useful life of the underlying asset. If a lease transfers ownership of the underlying asset or the cost of the right-of-use asset reflects that the Company expects to exercise a purchase option, the related right-of-use asset is depreciated over the useful life of the underlying asset. The right-of-use assets are presented in the statement of financial position under the caption “Property, plant and equipment”. 2.7 Impairment of assets At the end of each reporting period, the Company reviews the carrying amounts of its tangible and intangible assets to determine whether there is any indication that those assets have suffered an impairment loss. If any such indication exists, the recoverable amount of the asset is estimated in order to determine the extent of the impairment loss (if any). Where it is not possible to estimate the recoverable amount of an individual asset, the Company estimates the recoverable amount of the cash‑generating unit to which the asset belongs. Intangible assets with indefinite useful lives and intangible assets not yet available for use are tested for impairment at least annually, and whenever there is an indication that the asset may be impaired. Recoverable amount is the higher of fair value less costs to sell and value in use. In assessing value in use, the estimated future cash flows are discounted to their present value using a pre‑tax discount rate that reflects current market assessments of the time value of money and the risks specific to the asset for which the estimates of future cash flows have not been adjusted. If the recoverable amount of an asset (or cash‑generating unit) is estimated to be less than its carrying amount, the carrying amount of the asset (or cash‑generating unit) is reduced to its recoverable amount. An impairment loss is recognized immediately in profit or loss. Where an impairment loss subsequently reverses, the carrying amount of the asset (or a cash‑generating unit) is increased to the revised estimate of its recoverable amount, but so that the increased carrying amount does not exceed the carrying amount that would have been determined had no impairment loss been recognized for the asset (or cash‑generating unit) in prior years. A reversal of an impairment loss is recognized immediately in profit or loss. 2.8 Financial assets: investments (i) Classification The Company classifies its financial assets in the following measurement categories: those to be measured subsequently at fair value through profit or loss (FVTPL) and those to be measured at amortized cost. The classification depends on the Company’s business model for managing the financial assets and the contractual terms of the cash flows. Regular purchases and sales of financial assets are recognized on the trade date – the date on which the Company commits to purchase or sell the asset. Financial assets are derecognized when the rights to receive cash flows from the investments have expired or have been transferred and the Company has transferred substantially all risks and rewards of ownership. For assets measured at fair value, gains and losses will be recorded in profit or loss. (ii) Measurement At initial recognition, the Company measures a financial asset at its fair value plus, in case of a financial asset not at FVTPL, transaction costs that are directly attributable to the acquisition of the financial asset. Transaction costs of financial assets carried at FVTPL are expensed in profit or loss. The Company subsequently measures all equity investments at fair value. Dividends from such investments continue to be recognized in profit or loss as financial income when the Company’s right to receive payments is established. Changes in the fair value of financial assets at FVPL are recognized in financial income/expenses in the statement of profit or loss. The fair value of listed investments is based on current market prices. If the market for a financial asset is not active (and for unlisted securities), the Company establishes fair value by using valuation techniques. 2.9 Trade and other receivables Trade receivables are recognised initially at the amount of consideration that is unconditional. The Company holds the trade receivables with the objective to collect the contractual cash flows and therefore measures them subsequently at amortised cost using the effective interest method. Unless the impact of discounting is material, the nominal value is recognized. Trade receivables are recognized initially at their transaction price and are subsequently measured at amortized cost using the effective interest rate method, less provision for expected credit losses. For determining the expected credit losses, the Company applies the simplified approach permitted by IFRS 9, which requires lifetime losses to be recognized from initial recognition of the receivables. 2.10 Research and development incentive receivables Since the Company carries out extensive research and development activities, it benefits from a research and development incentive tax scheme in Belgium under which the research and development incentives can be refunded after five years if not offset against future income tax expense. These research and development incentives generally aim to partly reimburse expenditures incurred in our research and development efforts and are credited to the statement of profit or loss under the line “Other operating income” when the relevant expenditure has been incurred and there is a reasonable assurance that the research and development incentives are receivable. 2.11 Cash and cash equivalents Cash and cash equivalents includes cash in hand, deposits held at call with banks and other short term highly liquid investments with original maturities of three months or less and with an insignificant risk of changes in value. Bank overdrafts, if any, are shown within borrowings in current liabilities on the statement of financial position. Cash balances that are not available for use by the Company are presented as “restricted cash” in the statement of financial position. For the purpose of the statements of cash flows, cash and cash equivalents includes cash on hand and deposits held at call or short term maturity with banks (three months or less with insignificant risk of changes in value). 2.12 Shareholder’s equity An equity instrument is any contract that evidences a residual interest in the assets of an entity after deducting all of its liabilities. Equity instruments issued by the Company are recognized at the proceeds received, net of direct issue costs. The Company has never distributed any dividends to its shareholders. As of December 31, 2019, no profits were available for distribution. 2.13 Trade and other payables Payables after and within one year are measured at amortized cost, i.e., at the net present value of the payable amount. Unless the impact of discounting is material, the nominal value is recognized. 2.14 Provisions Provisions are recognized when the Company has a present obligation (legal or constructive) as a result of a past event, it is probable that the Company will be required to settle the obligation, and a reliable estimate can be made of the amount of the obligation. The amount recognized as a provision is the best estimate of the consideration required to settle the present obligation at the end of the reporting period, taking into account the risks and uncertainties surrounding the obligation. When a provision is measured using the cash flows estimated to settle the present obligation, its carrying amount is the present value of those cash flows (where the effect of the time value of money is material). When some or all of the economic benefits required to settle a provision are expected to be recovered from a third party, a receivable is recognized as an asset if it is reasonably certain that reimbursement will be received and the amount of the receivable can be measured reliably. 2.15 Retirement benefits The Company offers a post‑employment, death, disability and healthcare benefit scheme. All employees have access to these schemes. The death, disability and healthcare benefits granted to employees of the Company are covered by an external insurance company, where premiums are paid annually and charged to the income statement as they were incurred. The post‑employment pension plan granted to employees of the Company is a defined contribution plan under Belgian Law. Under defined contribution plans, the Company pays contributions based on salaries to organizations responsible for paying out pensions and social security benefits, in accordance with the laws and agreements applicable in each country. The Belgian defined contribution pension plans are by law subject to minimum guaranteed rates of return, historically 3.25% on employer contributions and 3.75% on employee contributions. These rates have been modified by the law of December 18, 2015 and effective for contribution paid as from 2016 to a new variable minimum return based on the OLO (‘Obligation Lineaire Obligaties’—Belgian Government Bond) rates, with a minimum of 1.75% and a maximum of 3.75%. Hence, from 2016 onwards, these plans are accounted for as defined benefit plans (see note 14). The liability recognized in the balance sheet is the present value of the defined benefit obligation less the fair value of plan assets. An independent actuary calculates the defined benefit obligation based on factors such as age, years of service and compensation (projected unit credit method). The present value of the defined benefit obligation is determined by discounting the estimated future cash outflows using interest rates of high‑quality corporate bonds denominated in the currency in which the benefits will be paid and with terms to maturity that approximate the term when the related liability is due. Current service costs are recognized in personnel expenses, which are included in Research and development expenses and in Selling, general and administrative expenses, and reflect the increase in the defined benefit obligation resulting from employee service in the current year. Past service costs are recognized immediately in personnel expenses. The net interest expense on the defined benefit liability is determined by applying the discount rate used to measure the defined benefit obligation at the beginning of the year to the then net defined benefit liability. Net interest expense is recognized in personnel expenses. Remeasurement gains and losses of the defined benefit obligation arising from experience adjustments and changes in actuarial assumptions are recognized immediately in other comprehensive income. 2.16 Short‑term employee benefits Short‑term employee benefits include payables and accruals for salaries and bonuses to be paid to the employees of the Company. They are recognized as expenses for the period in which employees perform the corresponding services. 2.17 Share‑based payments Equity‑settled share‑based payments to employees and others providing similar services are measured at the fair value of the equity instruments at the grant date. Details regarding the determination of the fair value of equity‑settled share‑based transactions are set out in note 13. The fair value determined at the grant date of the equity‑settled share‑based payments is expensed on a straight‑line basis over the vesting period, based on the Company’s estimate of equity instruments that will eventually vest, with a corresponding increase in equity. At the end of each reporting period, the Company revises its estimate of the number of equity instruments expected to vest. The impact of the revision of the original estimates, if any, is recognized in profit or loss such that the cumulative expense reflects the revised estimate, with a corresponding adjustment to the equity‑settled share‑based payment reserve. Where the terms of equity‑settled share‑based payments are modified, the minimum expense recognized is the expense that would have been recognized if the terms had not been modified. An additional expense is recognized for any modification that increases the total fair value of the share‑based payments, or is otherwise beneficial to the employee as measured at the date of modification. 2.18 Deferred revenue Current and non-current deferred revenue relates to cash received from commercial partnerships prior to completion of the earnings process. These payments are recognized as revenue over the estimated duration of the Company’s involvement in the research and development programs provided for under the terms of the agreements. IFRS 15 uses the term ‘contract liability’ to describe what might more commonly be known as ‘deferred revenue’, however IFRS 15 does not prohibit an entity from using alternative descriptions in the statement of financial position. The Company will continue to report its contract liabilities under the term ‘deferred revenue. 2.19 Income taxes Income tax expense represents the sum of the tax currently payable and deferred tax. The tax currently payable is based on taxable profit for the year. Taxable profit differs from profit as reported in the statement of profit and loss and other comprehensive income because of items of income or expense that are taxable or deductible in other years and items that are never taxable or deductible. The Company’s liability for current tax is calculated using tax rates that have been enacted or substantively enacted by the end of the reporting period. Deferred tax is recognized on temporary differences between the carrying amounts of assets and liabilities in the consolidated financial statements and the corresponding tax basis used in the computation of taxable profit (e.g. differences between carrying amounts under IFRS and the statutory tax basis). Deferred tax liabilities are generally recognized for all taxable temporary differences. Deferred tax assets are generally recognized for all deductible temporary differences to the extent that it is probable that taxable profits will be available against which those deductible temporary differences can be utilized. Such deferred tax assets and liabilities are not recognized if the temporary difference arises from goodwill or from the initial recognition (other than in a business combination) of other assets and liabilities in a transaction that affects neither the taxable profit nor the accounting profit. The carrying amount of deferred tax assets is reviewed at the end of each reporting period and reduced to the extent that it is no longer probable that sufficient taxable profits will be available to allow all or part of the asset to be recovered. Deferred tax assets and liabilities are measured at the tax rates that are expected to apply in the period in which the liability is settled or the asset realized, based on tax rates (and tax laws) that have been enacted or substantially enacted by the end of the reporting period. The measurement of deferred tax liabilities and assets reflects the tax consequences that would follow from the manner in which the Company expects, at the end of the reporting period, to recover or settle the carrying amount of its assets and liabilities. Deferred tax assets and deferred tax liabilities are offset if there is a legally enforceable right to offset current tax assets and liabilities and if they relate to income taxes imposed by the same authority on the same taxable entity or in different tax entities that intend to settle current tax assets and liabilities on a net basis or their tax assets and liabilities will be realized simultaneously. 2.20 Revenue and other operating income recognition Collaborations The Company adopted IFRS 15 on January 1, 2018. The Company elected the modified retrospective approach for the transition, which foresees that prior period figures remain as reported under the previous standard IAS 18, and the cumulative effect of applying IFRS 15 is recognized as an adjustment to the opening balance of equity as at the date of initial application (i.e., the beginning of the year 2018). In previous reporting periods, milestone payments were recognized under IAS 18 based upon the achievement of the milestone event, whereas under IFRS 15, the milestone payment is linked to a single performance obligation over the estimated service period. The revenue recognition of the upfront payments was not impacted by the transition from IAS 18 to IFRS 15. The cumulative effect of adopting IFRS 15 to the consolidated statement of financial position as of January 1, 2018 was as follows: (in thousands of €) Balance at December 31, 2017 Adjustments due to adoption IFRS 15 Balance at January 1, 2018 Assets Prepaid expenses € 2,338 € (255) € 2,083 Liabilities Deferred revenue — non-current € 1,435 € 378 € 1,813 Deferred revenue — current 8,635 2,272 10,907 Equity Accumulated losses € (100,568) € (2,395) € (102,962) The Company generates revenue from collaborations and strategic alliances. The Company applies a five-step model to determine when, how and at what amount revenue is to be recognized depending on whether certain criteria are met. 1. Identify the contracts In our current arrangements, the Company is licensing its Intellectual Property, providing research and development services and in the future, selling its products to collaborative partner entities. Revenue is generated through these arrangements via upfront payments, milestone payments based on development criteria, research and development service fees on an agreed full-time equivalent (FTE) basis and future sales based milestones and sales based royalties. 2. Identify performance obligations The Company has assessed that there is one single performance obligation in our material ongoing license and collaboration arrangements, being the transfer of a license combined with performance of research and development services. This is because we consider that the performance obligations cannot be distinct in the context of the contract as the license has no stand-alone value without the Company being further involved in the research and development collaboration and that there is interdependence between the license and the research and development services to be provided. We estimate that the Company’s activities during the collaboration are going to significantly add to Intellectual Property and thereby the value of the programs. 3. Determine the transaction price We have analyzed the transaction prices of our material ongoing license and collaboration arrangements currently composed of upfront payments, milestone payments and research and development service fees being delivered. Any variable consideration, such as development milestone payments that are promised in exchange for development services or the license of IP, is only included in the transaction price as from the moment the achievement of the related milestone event is highly probable (usually at the time of achievement of the milestone event). At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such milestones and any related constraint, and, if necessary, adjusts the estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catc

Critical accounting judgements

Critical accounting judgements and key sources of estimation uncertainty	12 Months Ended
	Dec. 31, 2019
Critical accounting judgements and key sources of estimation uncertainty
Critical accounting judgements and key sources of estimation uncertainty	3. Critical accounting judgements and key sources of estimation uncertainty In the application of the Company’s accounting policies, which are described above, the Company is required to make judgments, estimates and assumptions about the carrying amounts of assets and liabilities that are not readily apparent from other sources. The estimates and associated assumptions are based on historical experience and other factors that are considered to be relevant. Actual results may differ from these estimates. The estimates and underlying assumptions are reviewed on an ongoing basis. Revisions to accounting estimates are recognized in the period in which the estimate is revised if the revision affects only that period or in the period of the revision and future periods if the revision affects both current and future periods. The following areas are areas where key assumptions concerning the future, and other key sources of estimation uncertainty at the end of the reporting period, have a significant risk of causing a material adjustment to the carrying amounts of assets and liabilities within the next financial year. Critical judgements in applying accounting policies Revenue recognition The Company recognized revenue of €21.6 million on the basis of costs incurred and deferred revenue of €289.0 million related to a global collaboration and license agreement entered into with Cilag GmbH International, an affiliate of Janssen as of and for the year ended December 31, 2019. The Company received $500 million as upfront payment for this collaboration and license agreement, consisting of $300 million upfront cash payment for the collaboration and license agreement and $200 million as equity investment in the Company. The Company’s collaboration and license agreement has been determined as representing a single distinct performance obligation, due to the highly interdependent and interrelated nature of the development, manufacturing, and commercialization of the Licensed Compounds and Licensed Products. Fulfillment of the performance obligation occurs throughout the development, manufacturing, and commercialization phases of the Licensed Compounds and Licensed Products. The Company recognizes the consideration received as deferred revenue and subsequently recognizes revenue over the contract term (“over time”) based on a research and development cost input model using a percentage of completion method, whereby actual research and development costs incurred as part of the Company’s performance obligation is compared to the total expected research and development costs needed to satisfy the performance obligation at measurement date. Research and development cost accruals The Company recognizes costs of €44.0 million, as specified in note 15 to the financial statements, incurred for clinical trial activities and manufacturing of drug products, as research and development expenses based on an evaluation of its vendors’ progress toward completion of specific tasks. Payment timing may differ significantly from the period in which the costs are recognized as expense, resulting in clinical trial accruals recognized within Trade and other payables in the statement of financial position. Quantification of the research progress and the translation of the progress to these accruals requires judgment, because the progress is not directly observable. In estimating the vendors’ progress toward completion of specific tasks, the Company therefore uses data such as patient enrollment, clinical site activations and vendor information of actual costs incurred. This data is obtained through reports from or discussions with Company personnel and outside service providers as to the progress or state of completion of trials, or the completion of services. Costs are expensed over the service period the services are provided. Costs for services provided that have not yet been paid are recognized as accruals. Research and development cost accruals directly impact the revenue recognized, given the Company records revenue based on the percentage of completion method.

Intangible assets

Intangible assets	12 Months Ended
	Dec. 31, 2019
Intangible assets
Intangible assets	4. Intangible assets (in thousands of €) Opening balance as on January 1, 2017 Intangibles acquired separately Software licenses Total Cost € — € 93 € 93 Accumulated amortization — (76) (76) Book value at the beginning of the year — 17 17 Movements Additions — 6 6 Amortization — (10) (10) Balance as on December 31, 2017 Cost — 99 99 Accumulated amortization — (86) (86) Book value at year end — 13 13 Movements Additions — 62 62 Cost of disposals — (2) (2) Amortization — (19) (19) Accumulated ammortization on disposals — 2 2 Balance as on December 31, 2018 Cost — 159 159 Accumulated amortization — (103) (103) Book value at year end — 56 56 Movements Additions 39,881 262 40,143 Amortization — (38) (38) Balance as on December 31, 2019 Cost 39,881 421 40,302 Accumulated amortization — (141) (141) Book value at year end € 39,881 € 280 € 40,161 Intangible assets related to software licenses are amortized over 3 years. The intangibles assets held by the Company increased substantially as a result of the in-licensing of the ENHANZE® drug delivery technology from Halozyme. Under the terms of the agreement, the Company paid an upfront payment of $30 million, exercised the option to nominate an additional target (triggering a $10 million development milestone payment) and initiated a Phase 1 clinical trial using Halozyme's proprietary ENHANZE® drug delivery technology (triggering a $5 million development milestone payment). In line with its accounting policies, the Company has capitalized this upfront payment upon commencement of the in-license agreement. The development milestone payments have been capitalized when the development milestone was triggered. The Company performed an annual impairment review on the intangible assets not yet available for use. This review did not result in the recognition of an impairment charge. As of December 31, 2019, there are no commitments to acquire additional intangible assets, except as set forth in note 30. No intangible assets are pledged as security for liabilities nor are there any intangible assets whose title is restricted.

Property, plant and equipment

Property, plant and equipment	12 Months Ended
	Dec. 31, 2019
Property, plant and equipment.
Property, plant and equipment	5. Property, plant and equipment IT, office and lab Right-of-use assets Right-of-use assets Leasehold Lease (in thousands of €) equipment Buildings Vehicles improvements equipment (1) Total Opening balance as on January 1, 2017 Cost € 2,112 € — € — € — € — € 2,112 Accumulated depreciation (1,346) — — — — (1,346) Book value at the beginning of the year 766 — — — — 766 Movements Additions 346 — — — — 346 Cost of disposals (69) — — — — (69) Depreciation (425) — — — — (425) Accumulated depreciation on disposals 58 — — — — 58 Closing balance as on December 31, 2017 Cost 2,389 — — — — 2,389 Accumulated depreciation (1,713) — — — — (1,713) Book value at year end 676 — — — — 676 Movements Additions 370 — — — 253 623 Cost of disposals (47) — — — (46) Depreciation (463) — — — (11) (474) Accumulated depreciation on disposals 46 — — — 46 Closing balance as on December 31, 2018 Cost 2,712 — — — 253 2,965 Accumulated depreciation (2,130) — — — (11) (2,141) Book value at year end € 582 € — € — € — € 242 € 824 Adoption of IFRS 16 on January 1, 2019 € — € 2,338 € 452 — € — € 2,790 Movements Additions 765 4,553 525 808 29 6,680 Depreciation (460) (1,315) (233) (92) (28) (2,128) Closing balance as on December 31, 2019 Cost 3,477 6,891 977 808 282 12,435 Accumulated depreciation (2,590) (1,315) (233) (92) (39) (4,269) Book value at year end € 887 € 5,576 € 744 € 716 € 243 € 8,167 There are no commitments to acquire property, plant and equipment. Furthermore, no items of property, plant and equipment are pledged. See note 23 for information for leases where the Company is a lessee. (1) The Company has elected not to reassess whether a contract is, or contains, a lease at the date of initial application. Instead, for contracts entered into before the transition date, the Company relied on its assessment made applying IAS 17 and IFRIC 4 Determining whether an Arrangement contains a Lease.

Financial assets - noncurrent

Financial assets - noncurrent	12 Months Ended
	Dec. 31, 2019
Financial assets - noncurrent
Financial assets - noncurrent	6. Financial assets — non-current In March 2019, the Company entered into a license agreement with AgomAb Therapeutics NV for the use of HGF-mimetic SIMPLE Antibodies™, developed under the Company’s Innovative Access Program. In exchange for granting this license, the Company received a profit share in AgomAb Therapeutics NV. The Company assessed the accounting treatment and concluded that the license agreement is in scope of IFRS 15 and that any revenue should be recognized at once at the effective date of the agreement. The profit share has been designated as a non-current financial asset held at fair value through profit or loss. In March 2019, AgomAb Therapeutics NV secured €21.0 million in a Series A financing round. The Company used the post-money valuation of this Series A financing round and the number of outstanding shares in determining the initial fair value of the profit sharing instrument. In October 2019, a subsequent subscription to the Series A financing round increased the number of outstanding shares. The Company re-assessed the fair value of the profit sharing instrument, which resulted in a fair value gain on financial assets at fair value through profit or loss of €1.1 million.

Research and development incent

Research and development incentive receivables	12 Months Ended
	Dec. 31, 2019
Research and development incentive receivables
Research and development incentive receivables	7. Research and development incentive receivables Year Ended December 31, (in thousands of €) 2019 2018 2017 Research and development incentive receivables—current € 261 € 301 € 158 Research and development incentive receivables—non-current 8,566 4,883 3,033 € 8,827 € 5,184 € 3,191 On December 31, 2019, the Company has recorded a tax receivable of €8.8 million, compared to €5.2 million on December 31, 2018, in relation to a research and development incentive tax scheme in Belgium under which the research and development incentives can be refunded after five years if not offset against future income tax expense. The research and development incentives are recorded in other operating income (see note 18) in the consolidated statement of profit and loss and other comprehensive income. These amounts are expected to be gradually reimbursed in cash as from 2020 onwards.

Restricted cash

Restricted cash	12 Months Ended
	Dec. 31, 2019
Restricted cash
Restricted cash	8. Restricted cash Year Ended December 31, (in thousands of €) 2019 2018 2017 Non‑current restricted cash Rental guarantees € 630 € 251 € 256 Total non‑current € 630 € 251 € 256 Current restricted cash Escrow account < 1 year — 1,692 1,692 Total restricted cash € 630 € 1,943 € 1,948 On December 31, 2019, the Company had a total amount of €0.6 million of restricted cash: · A non‑current part for an amount of €0.6 million mainly relating to a deposit guarantee paid under the lease agreement for the laboratory and offices of the Company. · The current part of restricted cash related to an escrow account opened under an agreement with a third party involved in the collaboration with AbbVie. In 2019, this escrow account has been partially released to the Company and partially to the third party, as the work plan of the related collaboration agreement with AbbVie has been almost completed.

Trade and other receivables

Trade and other receivables	12 Months Ended
	Dec. 31, 2019
Trade and other receivables
Trade and other receivables	9. Trade and other receivables The trade and other receivables are composed of receivables which are detailed below: Year Ended December 31, (in thousands of €) 2019 2018 2017 VAT receivable € 1,121 € 496 € 317 Trade receivables 22,580 214 845 Other receivables 1,378 455 750 Interest receivable 2,081 556 — VLAIO grant receivable 955 1,165 930 € 28,115 € 2,886 € 2,842 The nominal amounts of all trade and other receivables approximate their respective fair values. The VAT receivable relates to VAT amounts to be recovered in the first quarter of 2020. Trade receivables correspond to amounts invoiced to the collaborators or strategic allies of the Company. On December 31, 2019, an amount of €0.1 million was due for more than 30 days, but still considered to be collectable. The Company applied the IFRS 9 simplified approach to measure expected credit losses, which uses a lifetime expected loss allowance for all receivables. To measure the expected credit losses, receivables have been grouped based on credit risk characteristics and the days past due. The provision for expected credit losses was not significant given that there have been no credit losses over the last three years and the high quality nature of our customers. As a result, no bad debt allowance was recorded nor were any trade receivables impaired on December 31, 2019 and December 31, 2018. The Flanders Innovation and Entrepreneurship Agency grant to receive consists of earned income from government grants for which no payments have been received but for which the relating expenditures have been incurred. For more information on the Flanders Innovation and Entrepreneurship Agency grants to receive, see note 18.

Financial assets - current

Financial assets - current	12 Months Ended
	Dec. 31, 2019
Financial assets - current
Financial assets - current	10. Financial assets — current On December 31, 2019, the current financial assets amounted to €1,004.5 million compared to €283.5 million on December 31, 2018. These current financial assets relate to: · Financial instruments in the form of money market funds with a recommended investment horizon of 6 months. These funds are highly liquid investments and can be readily converted into a known amount of cash, but because of their historical volatility these funds cannot be classified as cash and cash equivalents. Values recognized on the balance sheet are the fair values, with changes in fair value going through profit and loss. · USD term accounts with a maturity of six months. Please also refer to note 27 for more information on the financial instruments.

Cash and cash equivalents

Cash and cash equivalents	12 Months Ended
	Dec. 31, 2019
Cash and cash equivalents
Cash and cash equivalents	11. Cash and cash equivalents Year Ended December 31, (in thousands of €) 2019 2018 2017 Cash equivalents € 252,550 € 217,626 € 25,000 Cash and bank balances 78,732 63,414 165,867 € 331,282 € 281,040 € 190,867 On December 31, 2019, cash and cash equivalents amounted to €331.3 million compared to €281.0 million on December 31, 2018 and included cash equivalents and cash and bank balances held in different banks. Cash positions are invested with preferred financial partners, which are mostly considered to be high quality financial institutions with sound credit ratings. Policies are in place that limit the amount of credit exposure to any one financial institution (see also note 27).

Share capital and share premium

Share capital and share premium	12 Months Ended
	Dec. 31, 2019
Share capital and share premium
Share capital and share premium	12. Share capital and share premium Roll forward of number of shares outstanding: Number of shares outstanding on January 1, 2017 20,126,479 U.S. initial public offering on Nasdaq on May 17, 2017 5,865,000 Over-allotment option exercised by underwriters on May 19, 2017 879,750 Exercise of options in August 2017 5,000 Exercise of options in September 2017 15,000 Exercise of options in October 2017 1,400 Exercise of options in November 2017 106,782 U.S. second public offering on Nasdaq on December 13, 2017 4,440,000 Over-allotment option exercised by underwriters on December 14, 2017 666,000 Exercise of options in December 2017 75,230 Number of shares outstanding on December 31, 2017 32,180,641 Exercise of options in January 2018 111,727 Exercise of options in March 2018 113,075 Exercise of options in April 2018 34,039 Exercise of options in May 2018 5,900 Exercise of options in June 2018 5,393 Exercise of options in July 2018 469 Exercise of options in August 2018 2,300 Exercise of options in September 2018 5,913 U.S. third public offering on Nasdaq on September 18, 2018 3,475,000 Exercise of options in October 2018 556 Exercise of options in November 2018 9,768 Exercise of options in December 2018 30,531 Number of shares outstanding on December 31,2018 35,975,312 Exercise of options in January 2019 163,170 Share subscription from Johnson & Johnson Innovation Inc. 1,766,899 Exercise of options in February 2019 13,393 Exercise of options in March 2019 73,005 Exercise of options in April 2019 13,729 Exercise of options in May 2019 35,054 Exercise of options in June 2019 66,965 Exercise of options in July 2019 56 Exercise of options in August 2019 8,710 Exercise of options in September 2019 5,730 Exercise of options in October 2019 611 Global public offering on Euronext and Nasdaq on November 7, 2019 4,000,000 Over-allotment option exercised by underwriters on November 8, 2019 600,000 Exercise of options in November 2019 16,714 Exercise of options in December 2019 22,180 Number of shares outstanding on December 31,2019 42,761,528 New shares issued during 2017 On May 17, 2017, argenx SE offered 5,865,000 of its ordinary shares through an initial public offering in the United States in the form of ADSs at a price to the public of $17.00 per ADS, before underwriting discounts and commissions and offering expenses. On May 19, 2017, the underwriters of the offering exercised their over-allotment option to purchase 879,750 additional ADSs in full. As a result, argenx SE received €102.1 million of total gross proceeds from the offering, decreased by €9.6 million of underwriter discounts and commissions, and offering expenses, of which €8.9 million has been deducted from equity. The total net cash proceeds from this offering amounted to €92.5 million. On December 14, 2017, argenx SE offered 4,440,000 of its ordinary shares through a public offering in the United States in the form of ADSs at a price to the public of $52.00 per ADS, before underwriting discounts and commissions and offering expenses. On December 15, 2017, the underwriters of the offering exercised their over-allotment option to purchase 666,000 additional ADSs in full. As a result, argenx SE received €225.6 million of gross proceeds from this offering, decreased by €14.3 million of underwriter discounts and commissions, and offering expenses, of which €14.1 million has been deducted from equity. The total net cash proceeds from the Offering amounted to €211.3 million. For both offerings completed in 2017, the ADSs are evidenced by American Depositary Receipts (ADRs), and each ADS represents the right to receive one ordinary share. These ADSs are listed on the NASDAQ Global Select Market under the symbol “ARGX”. 203,412 new shares were also issued in 2017 as a result of the exercise of stock options under the argenx Employee Stock Option Plan. These issuances of shares resulted in a total of 32,180,641 ordinary shares with a nominal value of €0.1 per share on December 31, 2017. The extraordinary general meeting of the Company of November 7, 2017 had authorized the board of directors to issue up to a maximum of 20% of the then outstanding share capital for a period of 18 months, or up to a capital increase of €537,852.60 represented by 5,378,526 shares. The board of directors has issued 5,106,000 shares on the occasion of the U.S. public offering in December 2017 and as of December 31, 2017, the existing authorization allowed the issuance of up to 272,526 shares. New shares issued during 2018 On September 18, 2018, argenx SE offered 3,475,000 of its ordinary shares through a public offering in the United States in the form of ADSs at a price to the public of $86.50 per ADS, before underwriting discounts and commissions and offering expenses. As a result, argenx SE received €255.7 million of gross proceeds from this offering, decreased by €14.8 million of underwriter discounts and commissions, and offering expenses, of which €14.7 million has been deducted from equity. The total net cash proceeds from the offering amounted to €240.9 million. As a result of the exercise of options under the argenx Employee Stock Option Plan, 319,671 new shares were created in 2018. These issuances of shares resulted in a total of 35,975,312 ordinary shares, with a nominal value of €0.1 per share, on December 31, 2018. The annual general meeting of the Company on May 8, 2018 had authorized the board of directors to issue up to a maximum of 20% of the then outstanding share capital for a period of 18 months, or up to a capital increase of €648,790 represented by 6,487,896 shares. The board of directors has issued 3,475,000 shares on the occasion of the follow-on U.S. public offering in September 2018, and as of December 31, 2018, the existing authorization allowed the issuance of up to 3,012,896 shares. New shares issued during 2019 1,766,899 new shares were issued to Johnson & Johnson Innovation Inc., following the closing of the exclusive, global collaboration and license agreement for cusatuzumab (ARGX-110) with Cilag GmbH International, an affiliate of the Janssen Pharmaceutical Companies of Johnson & Johnson. The Company concluded that the share premium that Janssen paid above the closing price on the day of entering into the investment agreement (equal to an amount of €24.9 million) was paid because of the existing obligations to deliver development services under the terms of the collaboration agreement, and is therefore to be allocated to the single performance obligation (see also note 17). On November 7, 2019, argenx SE offered 4,000,000 of its ordinary shares through a global offering which consisted of (i) a public offering of 1,410,057 ADSs in the U.S. and certain other countries outside the European Economic Area (EEA) at a price of $121.00 per ADS, before underwriting discounts and commissions and offering expenses; and (ii) a concurrent private placement of 2,589,943 of ordinary shares in the EEA at an offering price of €109.18 per share, before underwriting discounts and commissions and offering expenses. On November 8, 2019, the underwriters of the offering exercised their over-allotment option to purchase 600,000 additional ADSs in full. As a result, argenx SE received €502.2 million of gross proceeds from this offering, decreased by €23.2 million of underwriter discounts and commissions, and offering expenses, of which €23.0 million has been deducted from equity. The total net cash proceeds from the offering amounted to €479.0 million. As a result of the exercise of options under the argenx Employee Stock Option Plan, 419,317 new shares were created in 2019. These issuances of shares resulted in a total of 42,761,528 ordinary shares, with a nominal value of €0.1 per share, on December 31, 2019. The annual general meeting of the Company on May 9, 2019 had authorized the board of directors to issue up to a maximum of 20% of the then outstanding share capital for a period of 18 months, or up to a capital increase of €760,110 represented by 7,601,101 shares. The board of directors has issued 4,600,000 shares on the occasion of the follow-on global offering in November 2019, and as of December 31, 2019, the existing authorization allows the issuance of up to 3,001,101 shares.

Share based payments

Share based payments	12 Months Ended
	Dec. 31, 2019
Share based payments
Share based payments	13. Share-based payments The Company has a stock options scheme for the employees of the Company and its subsidiaries. In accordance with the terms of the plan, as approved by shareholders, employees may be granted options to purchase ordinary shares at an exercise price as mentioned below per ordinary share. The Company has granted on June 28, 2019 a total of 423,487 stock options, on November 1, 2019 a total of 19,800 stock options and on December 20, 2019 a total of 921,885 stock options to its employees, Board members and consultants. The total number of stock options outstanding on December 31, 2019 totaled 4,358,069 compared to 3,536,651 on December 31, 2018 and 2,862,216 on December 31, 2017. No stock options were expired in the years ended December 31, 2019, 2018 and 2017. 419,317 stock options have been exercised in the year ended December 31, 2019 compared to 319,671 in the year ended December 31, 2018 and 203,412 in the year ended December 31, 2017. A total of 124,437 stock options have been forfeited in the year ended December 31, 2019 compared to 46,369 in the year ended December 31, 2018 and 2,369 in the year ended December 31, 2017. The stock options are granted to employees, consultants or directors of the Company and its subsidiaries. The stock options have been granted free of charge. Each employee’s stock option converts into one ordinary share of the Company upon exercise. No amounts are paid or payable by the recipient on receipt of the option. The options carry neither rights to dividends nor voting rights. Options may be exercised at any time from the date of vesting to the date of their expiry. The stock options granted vest, in principle, as follows: · 1/3rd of the stock options granted will vest on the first anniversary of the granting of the stock options, and · 1/24th of the remaining 2/3rd of the stock options granted will vest on the last day of each of the 24 months following the month of the first anniversary of the granting of the stock options. On November 25, 2019, at the extraordinary general meeting, the shareholders of the Company approved the amended stock option plan. The amended stock option plan authorizes the Board to also grant sign-on stock options, which vest as follows: · 1/4th of the stock options granted will vest on the first anniversary of the granting of the stock options, and · 1/36th of the remaining 3/4th of the stock options granted will vest on the last day of each of the 36 months following the month of the first anniversary of the granting of the stock options. No other conditions are attached to the stock options. The following share-based payment arrangements were in existence during the current and prior years and which are exercisable at the end of each period presented: Exercise price Outstanding per stock stock options on options December 31, Expiry date (in €) 2019 2018 2017 2020 € 3.95 7,210 18,200 36,960 2021 3.95 — — 2,850 2023 2.44 211,769 294,400 314,593 2024 2.44 96,696 117,733 135,890 2024 3.95 6,238 6,895 15,692 2024 7.17 335,067 407,061 516,100 2024 2.44 6,000 26,970 83,820 2025 11.44 39,000 39,000 39,000 2025 10.34 3,000 3,000 3,000 2025 9.47 185,832 226,323 235,514 2026 11.38 45,000 50,415 60,000 2026 11.47 219,791 257,616 282,310 2026 14.13 258,746 315,102 362,126 2027 18.41 108,613 114,019 120,536 2027 21.17 565,798 628,292 653,825 2023 80.82 94,100 94,600 — 2028 80.82 73,100 75,450 — 2023 86.32 366,260 369,760 — 2028 86.32 402,714 491,815 — 2024 113.49 111,690 — — 2029 113.49 279,760 — — 2029 113.49 19,800 2024/2029 (1) € 135.75 921,885 — — 4,358,069 3,536,651 2,862,216 (1) On December 20, 2019, the Company granted options for which the beneficiaries had a 60-day period to choose between a contractual term of five or ten years. 2019 2018 2017 Number of Weighted average Number of Weighted average Number of Weighted average stock options exercise price stock options exercise price stock options exercise price Outstanding at January 1 3,536,651 € 33.42 2,862,216 € 11.54 2,293,636 € 7.72 Granted 1,365,172 128.52 1,040,475 85.37 774,361 20.74 Exercised (419,317) 11.35 (319,671) 7.02 (203,412) 3.46 Forfeited (124,437) 88.92 (46,369) 30.44 (2,369) 12.52 Outstanding at December 31, 4,358,069 63.75 3,536,651 33.42 2,862,216 11.54 Exercisable at December 31, 2,203,476 € 22.59 1,859,315 € 9.62 1,598,829 € 6.80 The weighted average share price at the date of exercise of options exercised during the year ended December 31, 2019 was €110.99, compared to €66.93 during the year ended December 31, 2018 and €23.53 during the year ended December 31, 2017. The weighted average remaining contractual life of the stock options outstanding amounted to 7.27 years on December 31, 2019 compared to 7.82 years on December 31, 2018 and 8.03 years on December 31, 2017. The table below shows the weighted average remaining contractual life for each range of exercise price: Weighted average remaining Outstanding on contractual life Exercise price (in €) December 31, 2019 (in years) 2.44-3.95 327,913 3.95 7.17-9.47 520,899 5.32 10.34-14.13 565,537 6.59 18.41-21.17 674,411 7.88 80.82-86.32 936,174 6.43 113.49-135.75 1,333,135 9.41 The fair market value of the stock options has been determined based on the Black and Scholes model using the following assumptions: · The expected volatility corresponds to the calculated annual volatility of our shares since our initial public offering on Euronext Brussels on July 10, 2014 until the date of grant of the options. · The average expected option life is determined as a weighted average of the time from grant date to date of becoming exercisable and from grant date to expiry of the warrants. · Risk free interest rate equals the Belgium 10Year Bond Yield at the date of grant. · Expected dividends is considered 0% as we have no plan for distributing dividends and have no history of distributing dividends to shareholders. Below is an overview of the parameters used in relation to the determination of the fair value of the grants during 2019: Stock options granted in June 2019 Nov 2019 Dec 2019 Number of options granted 423,487 19,800 921,885 Average fair value of options (in EUR) € 63.45 € 57.69 € 65.72 Share price (in EUR) € 123.20 € 126.40 € 146.40 Exercise price (in EUR) € 113.49 € 113.49 € 135.75 Expected volatility 45.25 % 44.14 % 44.18 % Average expected option life (in years) 8.59 6.50 6.50 (1) Risk‑free interest rate 0.07 % (0.05) % 0.03 % Expected dividends — % — % — % (1) On December 20, 2019, the Company granted a total of 921,885 stock options. The beneficiary can choose between a contractual term of five or ten years. The average expected option life is currently estimated at six and a half years. This estimate will be reassessed once the acceptance period of 60 days has passed and the beneficiaries will have made a choice between a contractual term of five or ten years. The total fair value of the grant would range from €49.5 million (100% of the stock options at an expected option life of four years) to €60.6 million (100% of the stock options at an expected option life of six and a half years). Below is an overview of the parameters used in relation to the determination of the fair value of grants during 2018: Stock options granted in June 2018 Dec 2018 Number of options granted 178,900 861,575 Average fair value of options (in EUR) € 32.12 € 39.85 Share price (in EUR) € 72.00 € 82.20 Exercise price (in EUR) € 80.82 € 86.32 Expected volatility 45.50 % 46.19 % Average expected option life (in years) 7.36 7.83 Risk‑free interest rate 0.72 % 0.77 % Expected dividends — % — % Below in an overview of the parameter used in relation to the determination of the fair value of grants during 2017: Stock options granted in June 2017 Dec 2017 Number of options granted 120,536 653,825 Average fair value of options (in EUR) € 7.90 € 37.10 Share price (in EUR) € 17.76 € 53.50 Exercise price (in EUR) € 18.41 € 21.17 Expected volatility 36.6 % 36.1 % Average expected option life (in years) 10 10 Risk‑free interest rate 0.61 % 0.53 % Expected dividends — % — % The total share-based payment expense recognized in the consolidated statement of comprehensive income totaled €39.6 million for the year ended December 31, 2019, compared to €19.2 million for the year ended December 31, 2018 and €4.3 million for the year ended December 31, 2017.

Provision for employee benefits

Provision for employee benefits	12 Months Ended
	Dec. 31, 2019
Provision for employee benefits
Provision for employee benefits	14. Provisions for employee benefits Our personnel in Belgium participated in a defined contribution plan (extra-legal pension). The Belgian defined contribution pension plans were by law subject to minimum guaranteed rates of return, 3.25% on employer contributions and 3.75% on employee contributions. These rates, which apply as an average over the entire career, may be modified by Royal Decree. Therefore, those plans were basically accounted for as defined contribution plans. As a consequence of the law of December 18, 2015, minimum returns were guaranteed by the employer as follows: (a) for the contributions paid as from January 1, 2016, a new variable minimum return based on OLO rates, with a minimum of 1.75% and a maximum of 3.75%. In review of the low rates of the OLO in the last years, the return has been initially set to 1.75%; (b) for the contributions paid until end of December 2015, the previously applied legal returns as mentioned above, continue to apply until the leaving of the employees. In view of the minimum returns guarantees, the Belgian defined contribution plans classify as defined benefit plans as from end December 2015. The amounts recognized in the balance sheet are as follows: (in thousands of €) 2019 2018 2017 Defined benefit obligation € 1,789 € 1,277 € 1,007 Fair value of plan assets 1,725 1,270 982 Deficit / surplus (−) of funded obligations 64 7 25 Net liability (asset) € 64 € 7 € 25 The movement in the defined benefit obligation, plan assets, net liability and asset over the year is as follows: (in thousands of €) 2019 2018 2017 Defined benefit obligation at January 1 € 1,277 € 1,007 € 670 Service cost 379 336 352 Interest expense 19 15 11 Contributions by plan participants (167) (116) (148) Actuarial gains (-) / losses (+) 281 35 124 Benefits paid / transfers out — — (2) Defined benefit obligation at December 31 € 1,789 € 1,277 € 1,007 (in thousands of €) 2019 2018 2017 Fair value of plan assets at January 1 € 1,270 € 982 € 669 Interest income 19 16 10 Administrative costs & taxes (47) (32) (46) Contributions by company & participants 475 328 423 Contributions by plan participants (168) (116) (148) Actuarial gains (+) / losses (-) 176 92 76 Benefits paid / transfers out — — (2) Fair value of plan assets at December 31 € 1,725 € 1,270 € 982 In the income statement, current service cost and interest expense or income are included in the operating loss. The Company’s estimated employer contributions for 2019 amount to €0.3 million compared to €0.2 million in 2018 and €0.3 million in 2017. Plan assets on December 31, 2019, 2018 and 2017 consisted fully of insurance contracts and did not include direct positions in the Company’s shares or bonds, nor do they include any property used by the Company. The principal actuarial assumption on the balance sheet date (weighted averages based on outstanding defined benefit obligation) was: Actuarial assumption 2019 2018 2017 Discount rate 1.0 % 1.3 % 1.3 % The weighted average duration of the benefit obligations equals 19.32 years. Sensitivity analyses show the following effects: Sensitivity analysis Change in Impact on defined ‑ (in thousands of €) assumption benefit obligation % Discount rate -0.25 % Increase by 45.5 2.54 % Discount rate 0.25 % Decrease by (33.7) 1.88 % The above analyses were done on a mutually exclusive basis, and holding all other assumptions constant. Through its defined benefit plan, the Company is exposed to a number of risks, the most significant of which are detailed below: Asset volatility The plan liabilities are calculated using a discount rate set with reference to corporate bond yields; if plan assets underperform this yield, this will create a deficit. Changes in bond yields A decrease in corporate bond yields will increase plan liabilities, although this will be partially offset by an increase in the value of the plan’s bond holdings. Salary risk The majority of the plan’s benefit obligations are calculated by reference to the future salaries of plan members. As such, a salary increase of plan members higher than expected will lead to higher liabilities. Longevity risk Belgian pension plans provide for lump sum payments upon retirement. As such there is limited or no longevity risk. The weighted average age of the plan participants equals 46.2 years on December 31, 2019, compared to 43.8 years on December 31, 2018 and 46 years on December 31, 2017.

Trade and other payables

Trade and other payables	12 Months Ended
	Dec. 31, 2019
Trade and other payables
Trade and other payables	15. Trade and other payables Year Ended December 31, (in thousands of €) 2019 2018 2017 Trade payables € 9,360 € 6,007 € 4,395 Accruals for invoices to be received 49,069 18,145 4,046 Short‑term employee benefits 26,872 12,920 6,844 € 85,301 € 37,072 € 15,285 Trade payables correspond primarily to clinical and manufacturing activities. The fair value of trade payables approximates their carrying amount. The accruals for invoices to be received amount to €49.1 million for the year ended December 31, 2019, of which €44.0 million relate to invoices to be received from clinical manufacturing organizations for the manufacturing of drug products and from clinical research organizations. Short‑term employee benefits include payables and accruals for salaries and bonuses to be paid to the employees of the Company.

Tax liabilities

Tax liabilities	12 Months Ended
	Dec. 31, 2019
Tax liabilities
Tax liabilities	16. Tax liabilities The current tax liability amounts to €0.3 million for the year ended December 31, 2019 and corresponds primarily to the tax payable on the result of argenx US, Inc. in view of the transfer price agreements set up between argenx BV and argenx US, Inc. As part of its business restructuring, the Company transferred the legal ownership of its intellectual property rights from the Dutch argenx SE to its wholly owned Belgian subsidiary, argenx BV effective as of January 1, 2017, for an amount of €79.9 million. In 2019, the Company has obtained a tax ruling in Belgium which allows for a treatment of the aforementioned amount as a tax deductible cost in the Belgian subsidiary.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2019
Revenue
Revenue	17. Revenue Year Ended December 31, (in thousands of €) 2019 2018 2017 Upfront payments € 22,360 € 8,635 € 20,137 Milestone payments 28,085 11,440 9,677 Research and development service fees 19,338 1,407 6,601 € 69,783 € 21,482 € 36,415 For the years ended December 31, 2019 and 2018, the majority of the revenue was generated under the agreements with Janssen and AbbVie, each as described below. These agreements comprise elements of upfront payments, milestone payments based on development criteria and research and development fees. For the year ended December 31, 2019, €27.3 million related to the collaboration and license agreement with AbbVie was recognized in revenue on the basis of costs incurred for this program. Revenue recognized consisted of (i) €0.8 million related to the upfront payment received, (ii) €0.4 million related to development milestone payments received in previous years and (iii) €26.1 million related to a milestone achieved in 2019. The outstanding balance of deferred revenue amounts to €1.4 million of which €1.2 million is recognized as deferred revenue — current and €0.2 million as deferred revenue — non-current. For the year ended December 31, 2019, €21.6 million related to the collaboration and license agreement with Janssen was recognized in revenue on the basis of costs incurred for this program. Revenue recognized consisted of (i) €18.3 million related to the upfront payment received, (ii) €1.7 million related to the revenue recognition of deferred income triggered by the accounting treatment of the share subscription agreement at the time of signing of the agreement in December 2018 and (iii) €1.6 million related to a milestone achieved in 2019. The outstanding balance of deferred revenue amounts to €289.0 million of which €71.1 million is recognized as deferred revenue — current and €217.9 million as deferred revenue — non-current. In total, the Company recognized €1.2 million of revenue that was included in the deferred revenue balance at the beginning of the year. As of December 31, 2019, the unsatisfied performance obligations resulting from out-licensing agreements amounted to €290.4 million (compared to €2.2 million as of December 31, 2018). Management expects that 25% of the transaction price allocated to the unsatisfied performance obligations will be recognized as revenue during the next reporting period. The remaining 75% will be recognized in financial years 2021 until 2027. The amount disclosed above does not include variable consideration which is constrained. Research and development service fees increased by €17.9 million to €19.3 million for the year ended December 31, 2019 due to the research and development service fees recognized under the Janssen collaboration and license agreement. Below are summaries of the key collaborations. AbbVie In April 2016, the Company entered into a collaboration agreement with AbbVie S.À.R.L. (AbbVie) to develop and commercialize ARGX-115 (ABBV-151). Under the terms of the collaboration agreement, the Company was responsible for conducting and funding all ARGX‑115 (ABBV-151) research and development activities up to completion of IND enabling studies. The Company granted AbbVie an exclusive option, for a specified period following completion of IND enabling studies, to obtain a worldwide, exclusive license to the ARGX‑115 (ABBV-151) program to develop and commercialize products. The Company received an upfront, nonrefundable, non-creditable payment of $40 million (€35.1 million as of the date the payment was received) from AbbVie for the exclusive option to license ARGX‑115 (ABBV-151). The Company achieved two preclinical milestones, each of which triggered a $10.0 million payment (€8.9 million based on the exchange rate in effect as of the date the first milestone payment was received, and €8.7 million based on the exchange rate in effect as of the date the second milestone payment was received). In August 2018, AbbVie exercised its option and has assumed certain development obligations, being solely responsible for all research, development and regulatory costs relating to ARGX-115 based products. In March 2019, the Company achieved the first development milestone upon initiation of a first-in-human clinical trial, triggering a $30.0 million payment. Subject to the continuing progress of ARGX-115 (ABBV-151) by AbbVie, the Company is eligible to receive development, regulatory and commercial milestone payments in aggregate amounts of up to $110 million, $190 million and $325 million, respectively, as well as tiered royalties on sales at percentages ranging from the mid‑single digits to the lower teens, subject to customary reductions. The Company has the right, on a product‑by‑product basis to co‑promote ARGX‑115 (ABBV-151) based products in the European Economic Area and Switzerland and to combine the product with the Company’s own future immuno‑oncology programs. The co‑promotion effort would be governed by a co‑promotion agreement negotiated in good faith by the parties. AbbVie will fund further GARP‑related research by the Company for an initial period of two years. AbbVie will have the right to license additional therapeutic programs emerging from this research, for which the Company could receive associated milestone and royalty payments. With regard to its collaboration with AbbVie, the Company concluded as follows: · There is one single performance obligation under IFRS 15, that being the transfer of a license combined with performance of research and development activities. The Company concluded that the license is not distinct in the context of the contract. · The transaction price of these two agreements is currently composed of a fixed part, that being an upfront license fee, and a variable part, that being milestone payments and cost reimbursements of research and development activities delivered. Milestone payments are only included in the transaction price as from the moment the achievement of the related milestone event is highly probable (usually at the time of achievement of the milestone event). Sales-based milestones and sales-based royalties are a part of the Company’s arrangements but are not yet included in its revenues, as its programs with AbbVie is still in the development phase. · The transaction price has been allocated to the single performance obligation, and revenues have been recognized over the estimated service period based on a pattern that reflects the transfer of the license and progress to complete satisfaction of the research and development activities. This is because the transfer of the license is considered to be combined with the performance of research and development activities. Therefore, research and development milestone payments are variable considerations that are entirely allocated to the single performance obligation. · The Company has chosen an input model to measure the satisfaction of the single performance obligation that considers percentage of costs incurred for these programs (percentage of completion method). · Cost reimbursements received could be recognized in revenues when costs are incurred and agreed by the parties, as the Company is acting as a principal in the scope of its stake of the research and development activities of its ongoing license and collaboration agreements. Janssen In December 2018, the Company entered into a collaboration agreement with Cilag GmbH International, an affiliate of Janssen, to jointly develop and commercialize cusatuzumab. The Company has granted Janssen a license to the cusatuzumab program to develop, manufacture and commercialize products. For the U.S., the granted commercialization license is co-exclusive with argenx, while outside the U.S., the granted license is exclusive. Janssen and argenx will assume certain development obligations, and will be jointly responsible for all research, development and regulatory costs relating to the products. argenx will be eligible to receive potentially up to $1.3 billion in development, regulatory and sales milestones, in addition to tiered royalties, ranging from the low double digits to the high teens. Janssen will be responsible for commercialization worldwide. argenx retains the option to participate in commercialization efforts in the US, where the companies have agreed to share royalties on a 50/50 basis, and outside the U.S., Janssen will pay sales royalties ranging from the low double digits to the high teens to argenx. Under the terms of the agreement, Janssen committed to an upfront payment of $500 million consisting of a license payment of $300 million and a $200 million equity investment in the Company by subscribing to 1,766,899 new shares at a price of €100.02 per share, including an issuance premium. The agreement became effective in January 2019 following expiration of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act. In December 2019, the Company achieved the first development milestone, triggering a $25.0 million payment. With regard to this collaboration with Janssen, the Company concluded as follows: · There is one single performance obligation under IFRS 15, that being the transfer of a license combined with performance of research and development activities. The Company concluded that the license is not distinct in the context of the contract. Moreover, the Company concluded that the share premium that Janssen paid above the closing price on the day of entering into the investment agreement (being December 2, 2018) was paid because of the existing obligations to deliver development services under the terms of the collaboration agreement, and is therefore to be allocated to the single performance obligation. · The transaction price of this agreement is currently composed of a fixed part, that being an upfront license fee and the share premium, and a variable part, that being milestone payments and cost reimbursements of research and development activities delivered. Milestone payments are only included in the transaction price as from the moment the achievement of the related milestone event is highly probable (usually at the time of achievement of the milestone event). Sales-based milestones and sales-based royalties are a part of the Company’s arrangements but are not yet included in its revenues, as its program with Janssen are still in the development phase. · The transaction price has been allocated to the single performance obligation, and revenues have been recognized over the estimated service period based on a pattern that reflects the transfer of the license and progress to complete satisfaction of the research and development activities. This is because the transfer of the license is considered to be combined with the performance of research and development activities. Therefore, research and development milestone payments are variable considerations that are entirely allocated to the single performance obligation. · The Company has chosen an input model to measure the satisfaction of the single performance obligation that considers percentage of costs incurred for these programs (percentage of completion method). · Cost reimbursements received are recognized in revenues when costs are incurred and agreed by the parties, as the Company is acting as a principal in the scope of its stake of the research and development activities of its ongoing license and collaboration agreements.

Other operating income

Other operating income	12 Months Ended
	Dec. 31, 2019
Other operating income
Other operating income	18. Other operating income Year Ended December 31, (in thousands of €) 2019 2018 2017 Grants € 2,289 € 1,842 € 422 Research and development incentives 4,818 2,151 983 Payroll tax rebates 5,694 3,756 3,436 € 12,801 € 7,749 € 4,841 Grants The Flanders Innovation and Entrepreneurship Agency provided the Company with several grants. On December 31, 2019, the situation of the grants received by the Company reflected the expenses incurred by the Company in the various research and development projects sponsored by Flanders Innovation and Entrepreneurship Agency. On December 31, 2019, the Company had two ongoing grant research projects: (Amounts presented in thousands of €) Flanders Innovation & Entrepreneurship - VLAIO 1 Grantor: Flanders Innovation & Entrepreneurship Agency Start date: 01/11/2017 End date: 31/10/2020 Amount granted and approved: € 2,527 Amount recognized: 845 Flanders Innovation & Entrepreneurship - VLAIO 2 Grantor: Flanders Innovation & Entrepreneurship Agency Start date: 01/05/2018 End date: 31/10/2020 Amount granted and approved: € 2,634 Amount recognized: 1,411 No conditions related to the above government grants were unfulfilled, nor were there any contingencies related thereon at the date of the approval of these consolidated financial statements, except for those described in note 29 of this report. Other Incentives Research and development incentives The Company has accounted for a tax receivable of €4.8 million in the year ended December 31, 2019, compared to €2.2 million in the year ended December 31, 2018, following a research and development tax incentive scheme in Belgium according to which the incentive will be refunded after a five year period, if not offset against the current tax payable over the period (see also note 7). Payroll tax rebates The Company accounted for €5.7 million payroll tax rebates in the year ended December 31, 2019, compared to €3.8 million in the year ended December 31, 2018, as a reduction in withholding income taxes for its highly‑qualified personnel employed in its research and development department.

Segment reporting

Segment reporting	12 Months Ended
	Dec. 31, 2019
Segment reporting
Segment reporting	19. Segment reporting The Company operates from the Netherlands, Belgium, the United States of America and Japan. Revenues are invoiced by the subsidiary in Belgium and are generated by clients geographically located as shown in the table below. Revenue from external customers Year ended December 31, (in thousands of €) 2019 2018 2017 Netherlands € € 470 € 628 Belgium 1,498 — — Denmark 436 1,136 6,240 Switzerland 40,593 912 2,486 United States — — 1 Luxembourg 27,256 18,964 27,060 Total € 69,783 € 21,482 € 36,415 Information about major clients: The Company received €69.8 million of revenue from its external customers in the year ended December 31, 2019 compared to €21.5 million over the same period in 2018, of which €40.6 million came from the Company’s largest client, €27.3 million from its second largest client and €1.5 million from its third largest client, compared to respectively €19.0 million, €1.1 million and €0.9 million in the year ended December 31, 2018. For a detailed description of our key collaborations, see note 17. The non-current assets of the Company are geographically located as shown in the table below: Non-current assets Year ended December 31, (in thousands of €) 2019 2018 2017 Netherlands € 1 € 1 € 1 Belgium 56,777 5,967 4,103 United States 3,058 47 — Japan 284 — — Total € 60,120 € 6,015 € 4,104

Research and development expens

Research and development expenses	12 Months Ended
	Dec. 31, 2019
Research and development expenses
Research and development expenses	20. Research and development expenses Year Ended December 31, (in thousands of €) 2019 2018 2017 Personnel expense € 45,733 € 26,519 € 16,473 External research and development expenses 137,050 48,859 27,893 Materials and consumables 2,027 1,464 1,562 Depreciation and amortization 1,641 494 446 Other expenses 11,214 6,273 5,366 € 197,665 € 83,609 € 51,740

Selling, general and administra

Selling, general and administrative expenses	12 Months Ended
	Dec. 31, 2019
Selling, general and administrative expenses
Selling, general and administrative expenses	21. Selling, general and administrative expenses Year Ended December 31, (in thousands of €) 2019 2018 2017 Personnel expense € 40,082 € 18,292 € 6,745 Consulting fees 5,624 3,646 3,289 Marketing costs 10,719 1,826 — Supervisory board 2,792 1,088 621 Office costs 5,352 2,619 1,793 € 64,569 € 27,471 € 12,448

Personnel expenses

Personnel expenses	12 Months Ended
	Dec. 31, 2019
Personnel expenses
Personnel expenses	22. Personnel expenses The personnel expenses mentioned in note 20 and 21 above are as follows: Year Ended December 31, (in thousands of €) 2019 2018 2017 Short ‑ term employee benefits—Salaries € 32,866 € 18,617 € 12,149 Short ‑ term employee benefits—Social Security 3,555 2,213 1,504 Post ‑ employment benefits 748 441 291 Termination benefits 644 96 8 Share ‑ based payment 37,208 18,527 3,985 Employer social security contributions stock options 10,794 4,918 5,281 € 85,815 € 44,812 € 23,218 The post‑employment benefits relate to the pension plans the Company has in place for its employees. The number of full‑time equivalents (FTE) employees by department is presented below: Year Ended December 31, Number of FTE 2019 2018 2017 Research and development 116.9 74.4 56.8 Selling, general and administrative 69.2 29.5 14.7 186.1 103.9 71.5 These FTE’s are working outside the Netherlands.

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases
Leases	23. Leases The statement of financial position shows the following amounts relating to leases: As on As on December 31, January 1, In thousands of € 2019 2019 Right-of-use assets Buildings € 5,576 € 2,338 Vehicles 744 525 Equipment 243 242 € 6,564 € 3,105 Lease liabilities Current € 1,974 € 1,078 Non-current 4,540 1,712 € 6,514 € 2,790 Additions to the right-of-use assets amounted to €5.1 million for the year ended December 31, 2019. The table below shows a maturity analysis of the lease liabilities as on December 31, 2019: (in thousands of €) Less than 1 year 1-3 years 3-5 years More than 5 years Total contractual cash flows Carrying amount Lease liabilities € 2,205 € 3,137 € 1,251 € 432 € 7,025 € 6,514 The statement of profit or loss and other comprehensive income shows the following amounts relating to leases: Year Ended December 31, In thousands of € 2019 2018 2017 Depreciation charges Buildings € 1,315 € — € — Vehicles 233 — — Equipment 28 11 — € 1,576 € 11 € — Interest expense (included in finance cost) € 105 € — € — Expense relating to short-term leases 123 — — Expense relating to leases of low-value assets that are not shown above as short-term leases 5 — — The total cash outflow for leases in 2019 was €1.6 million. The Company’s new accounting policy for leases is described in note 2.6. The Company did not enter into any lease agreement with variable lease payments or residual value guarantees. The Company has leases that include extension options. These options provide flexibility in managing the leased assets and align with the Company’s business needs. The Company exercises judgement in deciding whether it is reasonably certain that the extension options will be exercised. The Company leases offices and laboratory space in Zwijnaarde, Belgium. The contract contains an extension option for three years. The Company also leases office space in Boston, Massachusetts. The contract contains an extension option for five years. The Company has entered into an additional lease for office space in Tokyo, Japan in January 2020. The minimum lease term of three years and two months results in a contractually agreed cash outflow of ¥ 233.5 million (€1.9 million).

Financial result and exchange g

Financial result and exchange gains/(losses)	12 Months Ended
	Dec. 31, 2019
Financial result and exchange gains/(losses)
Financial result and exchange gains/(losses)	24. Financial result and exchange gains/(losses) Year Ended December 31, (in thousands of €) 2019 2018 2017 Interest income on bank deposits € 7,874 € 1,371 € 165 Net gains on current financial assets at FVTPL 6,525 2,323 210 Realized gain on non-current financial assets — — 875 Financial income 14,399 3,694 1,250 Financial expense (124) — — Realized exchange gains/(losses) (338) 1,355 — Unrealized exchange gains/(losses) 6,404 10,953 (5,797) Exchange gains/(losses) 6,066 12,308 (5,797) The exchange gains of €6.1 million for the year ended December 31, 2019 were primarily attributable to unrealized exchange rate gains on our cash and cash equivalents and current financial assets position in USD due to the favorable fluctuation of the USD exchange rate over the period.

Income tax expense

Income tax expense	12 Months Ended
	Dec. 31, 2019
Income tax expense
Income tax expense	25. Income tax expense The income tax expense for the year can be reconciled to the accounting loss as follows: Year Ended December 31, (in thousands of €) 2019 2018 2017 Loss before taxes (158,213) (65,847) (27,479) Income tax calculated at 25% 39,553 16,462 6,870 Effect of expenses that are not deductible in determining taxable results (7,701) (3,934) (1,141) Effect of stock issue expenses that are not deductible in determining taxable results 5,750 3,716 5,754 Effect of concessions (R&D incentives and grants) 572 430 453 Effect of tax losses carried forward not recognized (Netherlands) (356) — — Effect of usage of tax losses carried forward not previously recognized (Netherlands) — — 19,378 Effect of tax losses carried forward not recognized (Belgium) (11,314) (5,511) (27,413) Effect of adjustments for current tax of prior periods (Belgium) (3,876) — — Effect of change in corporate tax rate on deferred tax asset not previously recognized (Belgium) — — 373 Effect of different tax rates in jurisdictions in which the company operates (52) (15) (517) Deferred tax asset other than loss carryforwards not recognized (27,341) (11,968) (4,363) Other 13 26 9 Income tax expense recognized in the consolidated statement of profit and loss € (4,752) € (794) € (597) The tax rate used for the 2019, 2018 and 2017 reconciliations above is the corporate income tax rate of 25% payable by corporate entities in the Netherlands. The unrecognized deferred tax asset on deductible temporary differences and unused tax losses amounts to €40.0 million on December 31, 2019, compared to €29.3 million on December 31, 2018. Deferred tax have been measured using the effective rate that will apply in Belgium (25%). The Company has unused tax losses carried forward for an amount of €160.0 million on December 31, 2019 (compared to €117.1 million on December 31, 2018), of which €1.4 million will expire in 2028. This, combined with other temporary differences, resulted in a net deferred tax asset position. Due to the uncertainty surrounding the Company’s ability to realize taxable profits in the near future, the Company did not recognize any deferred tax assets. As part of its business restructuring, the Company transferred the legal ownership of its intellectual property rights from the Dutch argenx SE to its wholly owned Belgian subsidiary, argenx BV, effective as of January 1, 2017, for an amount of €79.9 million. In 2019, the Company has obtained a tax ruling in Belgium which allows for a treatment of the aforementioned amount as a tax deductible cost in the Belgian subsidiary.

Loss per share

Loss per share	12 Months Ended
	Dec. 31, 2019
Loss per share
Loss per share	26. Loss per share Year Ended December 31, (in thousands of €) 2019 2018 2017 Loss of the year € (162,965) € (66,641) € (28,076) Weighted average number of shares outstanding 38,619,121 33,419,356 24,609,536 Basic and diluted loss per share (in €) € (4.22) € (1.99) € (1.14) Earnings/losses per ordinary share are calculated by dividing the loss for the period by the weighted average number of ordinary shares during the year. As the Company is suffering operating losses, options have an anti‑dilutive effect. As such, there is no difference between basic and diluted earnings/losses per ordinary share. There are no other instruments that could potentially dilute earnings per ordinary share in the future.

Financial instruments and finan

Financial instruments and financial risk management	12 Months Ended
	Dec. 31, 2019
Financial instruments and financial risk management
Financial instruments and financial risk management	27. Financial instruments and financial risk management Overview of financial instruments This note provides information about the Company’s financial instruments, including: · an overview of all financial instruments by category · specific information about each type of financial instrument · information about determining the fair value of the instruments, including judgements and estimation uncertainty involved. · information on the financial risk management and capital management. Measurement category Carrying amount Year Ended December 31, (in thousands of €) 2019 2018 2017 (1) Financial assets — non-current FVTPL € 2,596 1 € 1 Research and development incentive receivables — non-current Amortised cost 8,566 4,883 3,033 Restricted cash — non-current Amortised cost 630 251 256 Trade and other receivables Amortised cost 28,115 2,886 2,842 Prepaid expenses Amortised cost 9,022 2,995 2,338 Financial assets—current FVTPL 1,004,539 283,529 168,907 Research and development incentive receivables — current Amortised cost 261 301 158 Restricted cash — current Amortised cost — 1,692 1,692 Cash and cash equivalents Amortised cost 331,282 281,040 190,867 Trade and other payables Amortised cost 85,301 37,072 15,285 (1) The Company adopted IFRS 9 on January 1, 2018. Under IAS 39, non-current financial assets were measured as “Available for sale”. Current financial assets included collective investment funds nominated in € and $ that are not considered as cash equivalents and of which the underlying investments include bonds and other international debt securities. The average credit rating of the underlying instruments is BBB or higher. The maximum exposure to credit risk is the carrying value at reporting date. These investment funds are recognized at fair value in the Company’s consolidated financial statements (level 1). The fair value corresponds to the quoted market price and can therefore be classified as a level 1 fair value measurement. The net asset value (NAV) of the funds is available on a daily basis. Any difference between amounts invested and fair value at reporting date is booked in Profit & Loss. Due to the current nature of the financial liabilities, the nominal value of all financial liabilities presented above approximates their fair value. The Company carried the following assets at fair value on December 31, 2019, 2018 and 2017 respectively: At December 31,2019 (in thousands of €) Level 1 Level 2 Level 3 Non-current financial assets € € € 2,596 Current financial assets 1,004,539 Assets carried at fair value € 1,004,539 € — € 2,596 At December 31,2018 (in thousands of €) Level 1 Level 2 Level 3 Non-current financial assets € € € 1 Current financial assets 283,529 Assets carried at fair value € 283,529 € — € 1 At December 31,2017 (in thousands of €) Level 1 Level 2 Level 3 Non-current financial assets € € € 1 Current financial assets 168,907 Assets carried at fair value € 168,907 € — € 1 During the disclosed calendar year no transfers occurred between the applicable categories. In March 2019, the Company entered into a license agreement with AgomAb Therapeutics NV for the use of HGF-mimetic SIMPLE Antibodies™, developed under the Company’s Innovative Access Program. In exchange for granting this license, the Company received a profit share in AgomAb Therapeutics NV. The profit share has been designated as a non-current financial asset held at fair value through profit or loss. Since AgomAb Therapeutics NV is a private company, the valuation of the profit share is based on level 3 assumptions. Capital risk The Company manages its capital to ensure that it will be able to continue as a going concern. The capital structure of the Company consists of equity attributed to the holders of equity instruments of the Company, such as capital, reserves and accumulated losses as mentioned in the consolidated statement of changes in equity. The Company makes the necessary adjustments in the light of changes in the economic circumstances, risks associated to the different assets and the projected cash needs of the current and projected research activities. On December 31, 2019, cash and cash equivalents amounted to €331.3 million and total capital amounted to €1,312.8 million. The current cash situation and the anticipated cash generation are the most important parameters in assessing the capital structure. The Company’s objective is to maintain the capital structure at a level to be able to finance its activities for at least twelve months. Cash income from existing and new partnerships is taken into account and, if needed and possible, the Company can issue new shares or enter into financing agreements. Credit risk Credit risk refers to the risk that a counterparty will default on its contractual obligations resulting in financial loss to the Company. The Company has adopted a policy of only dealing with creditworthy counterparties and obtaining sufficient collateral, where appropriate, as a means of mitigating the risk of financial loss from defaults. Concentrations in credit risk are determined based on an analysis of counterparties and their importance on the overall outstanding contractual obligations at year end. The Company has a limited number of collaboration partners and therefore has a significant concentration of credit risk. However, it has policies in place to ensure that credit exposure is kept to a minimum and significant concentrations of credit exposure are only granted for short periods of time to high credit quality collaboration partners. Credit exposure is controlled by counterparty limits that are reviewed and approved by management annually. Cash and cash equivalents and short‑term deposits are invested with several highly reputable banks and financial institutions. The Company holds its cash and cash equivalents mainly with different banks which are independently rated with a minimum rating of ‘A-’. The Company also holds short term investment funds in the form of money market funds with a recommended investment horizon of 6 months or shorter but with a low historical volatility. These money market funds are highly liquid investments, can be readily convertible into a known amount of cash. Since they are a basket of funds there is no individual credit risk involved. The average credit rating of the underlying instruments for the investment funds is BBB or higher. The maximum credit risk, to which the Company is theoretically exposed as at the balance sheet date, is the carrying amount of the financial assets. At the end of the reporting period no financial assets were past due, consequently no financial assets were subject to impairment. Liquidity risk The Company manages liquidity risk by maintaining adequate reserves, by continuously monitoring forecast and actual cash flows, and by matching the maturity profiles of financial assets and liabilities. The Company’s main sources of cash inflows are obtained through capital increases and collaboration agreements. This cash is invested in savings accounts, term accounts and short term investment funds in the form of money market funds. These money market funds represent the majority of the Company’s available sources of liquidity however since all of these are immediately tradable and convertible in cash they have a limited impact on the liquidity risk. All financial liabilities (principally trade and other payables as disclosed in note 27) have a maturity within 3 months unless otherwise disclosed in these consolidated financial statements. Interest rate risk The only interest‑bearing financial assets are cash at banks on deposit and term accounts. For the year ended December 31, 2019, if applicable interest rates would increase/decrease by 25 basis points, this would have a positive/negative impact of €2.0 million (compared to €0.3 million for the year ended December 31, 2018 and €0.3 million for the year ended December 31, 2017). Foreign exchange risk The Company undertakes transactions denominated in foreign currencies; consequently, exposures to exchange rate fluctuations arise. The Company is mainly exposed to the U.S. Dollar, Japanse yen, British pound and Swiss franc. To limit this risk, the Company attempts to align incoming and outgoing cash flows in currencies other than EUR. The net exposure to exchange differences of the monetary assets (being cash, cash equivalents and current financial assets) of the Company at the end of the reporting period are as follows: At December 31, (in thousands of €) 2019 2018 2017 USD 821,916 312,831 147,169 JPY 488 — — GBP 4 2 406 CHF 1 4 25 On December 31, 2019, if the USD/EUR exchange rate would have increased/decreased by 10%, this would have had a negative/positive impact of €74.72 million (compared to €28.44 million on December 31, 2018). On December 31, 2019, if the exchange rate for other currencies would have increased/decreased by 10% , this would have had no significant impact.

Related party transactions

Related party transactions	12 Months Ended
	Dec. 31, 2019
Related party transactions
Related party transactions	28. Related party transactions Balances and transactions between the Company and its subsidiaries, which are related parties of the Company, have been eliminated on consolidation and are not disclosed in this note. There were no significant transactions with related parties during the period, other than compensation of key management personnel. Compensation of key management personnel Key management personnel of the Company is composed of the Chief Executive Officer, the Chief Financial Officer, the Chief Operating Officer, the Chief Scientific Officer, the Chief Medical Officer, the Vice President of Corporate Development & Strategy and the General Counsel. The remuneration of the key management personnel during the year was as follows: Year Ended December 31, (in thousands of €) 2019 2018 2017 Short term employee benefits € 4,437 € 4,236 € 3,126 Post employment benefits 144 153 115 Termination benefits 470 — — Share ‑ based payment (1) 21,847 13,363 12,041 Employer social security contributions stock options (2) 9,160 2,792 3,073 € 36,058 € 20,544 € 18,355 (1) Amount shown represents the expenses with respect to the option awards granted in the year, measured using the Black Scholes formula. The share-based payment expense recognized in the consolidated statement of comprehensive income totaled €14.4 million for the year ended December 31, 2019, compared to €10.7 million for the year ended December 31, 2018 and €2.3 million for the year ended December 31, 2017 (2) The Company incurs employer social security costs with respect to the option awards granted to certain members of the executive management. The amount of employer social security costs depends on the actual economic value realized and therefore varies based on our stock price. At each reporting date, the Company makes a calculation of the exposure. Remuneration of the executive directors The tables below show the remuneration received by executive directors for the years ended December 31, 2019, 2018 and 2017 (in €). Eric Castaldi served as a member of our board until April 26, 2017. A scenario analysis based on best practice clause II.2.1. of the Dutch Corporate Governance Code was made. Executive directors have met each of their bonus targets previously established by the non-executive directors during the years ended December 31, 2019, 2018 and 2017 and the full bonus was granted in the same year. Pension 2017 Base salary Bonus contributions Social security costs ESOP (1) Other (2) Total Tim Van Hauwermeiren 303,941 301,635 14,315 9,459 2,968,195 9,601 3,607,146 Eric Castaldi 271,344 173,284 62,335 254,732 4,089,209 14,979 4,865,883 Total 575,285 474,919 76,650 264,191 7,057,404 24,580 8,473,029 Pension 2018 Base salary Bonus contributions Social security costs ESOP (1) Other (2) Total Tim Van Hauwermeiren 500,000 284,600 15,102 10,011 3,559,200 33,855 4,402,768 Total 500,000 284,600 15,102 10,011 3,559,200 33,855 4,402,768 Pension 2019 Base salary Bonus contributions Social security costs ESOP (1) Other (2) Total Tim Van Hauwermeiren 525,000 326,288 21,532 10,587 5,257,360 11,558 6,152,325 Total 525,000 326,288 21,532 10,587 5,257,360 11,558 6,152,325 (1) Amount shown represents the expenses with respect to the option awards granted in the year, measured using the Black Scholes formula, and the employer social security costs with respect to the option awards granted to certain members of the executive management. The amount of employer social security costs depends on the actual economic value realized and therefore varies based on our stock price. At each reporting date, the Company makes a calculation of the exposure. (2) Consists of rent paid by the Company, costs attributable to the lease of a company car and employer-paid medical insurance premiums. The table below shows the number of stock options granted to the executive directors during the years ended December 31, 2019, 2018 and 2017 and their exercise price equal to the fair market value upon date of grant, and the stock options exercised during 2019, 2018 and 2017. 2017 ESOPs Term Exercise price Exercised Tim Van Hauwermeiren 80,000 10 years 21.17 2.44 65,380 Eric Castaldi 43,200 years 21.17 Total 123,200 65,380 2018 ESOPs Term Exercise price Exercised Tim Van Hauwermeiren 80,000 10 years 86.32 7.17 40,000 Total 80,000 40,000 2019 ESOPs Term Exercise price Exercised Tim Van Hauwermeiren 80,000 10 years 135.75 7.17 30,000 Total 80,000 30,000 The table below shows the stock options held at the start of the year ended December 31, 2019, the stock options granted to executive directors which have vested during the year ended December 31, 2019 and the stock options to vest in the years until 2022. Total Total options options Options held on options options held on vested Options Options Options Options January 1, granted in exercised in December 31, until Exercise vested in Exercise to vest Exercise to vest Exercise to vest Exercise Name 2019 2019 2019 2019 2018 price 2019 price 2020 price 2021 price 2022 price Tim Van Hauwermeiren 336,200 80,000 (30,000) 386,200 35,000 7.17 30,600 9.47 43,056 6,944 20,400 10,200 26,667 26,666 21.17 26,667 21.17 21.17 26,667 86.32 26,666 86.32 26,667 86.32 26,667 135.75 26,666 135.75 26,667 135.75 The table below shows the remaining term of the options held by the executive directors on December 31, 2019. Name Number of options Remaining term at December 31, 2019 (rounded up) Tim Van Hauwermeiren 35,000 5.0 years 30,600 6.0 years 50,000 6.5 years 30,600 7.0 years 80,000 8.0 years 80,000 9.0 years 80,000 10.0 years Stock options are granted to the executive directors by the Board based on the recommendation of the Remuneration and Nomination Committee and the option allocation scheme established by the Board pursuant to the argenx Employee Stock Option Plan. Remuneration of non-executive directors The following table sets forth the information regarding the compensation earned by our non‑executive directors during the years ended December 31, 2019, 2018 and 2017: 2019 2018 2017 Peter Verhaeghe € 77,500 € 77,500 € 77,500 David L Lacey 50,000 50,000 50,000 Werner Lanthaler 55,000 55,000 55,000 Pamela Klein 42,500 42,500 42,500 Don Debethizy 52,500 52,500 52,500 A.A. Rosenberg 50,000 42,500 42,500 James M. Daly 50,000 35,000 — Total € 377,500 € 355,000 € 320,000 The table below shows the number of stock options granted to the non-executive directors during the years ended December 31, 2019, 2018 and 2017 and their exercise price, based on the 30 day average stock price prior to their date of grant, and the stock options exercised during the years ended December 31, 2019, 2018 and 2017. 2017 ESOPs Term Exercise price Exercised David L Lacey 15,000 10 years 21.37 Total 15,000 — 2018 ESOPs Term Exercise price Exercised James M. Daly 15,000 10 years 80.82 Peter Verhaeghe 10,000 10 years 86.32 David L Lacey 10,000 10 years 86.32 Werner Lanthaler 10,000 10 years 86.32 2.44 3,566 7.17 5,000 2.44 10,850 11.38 5,556 Don Debethizy 10,000 10 years 86.32 Pamela Klein 10,000 10 years 86.32 A.A. Rosenberg 10,000 10 years 86.32 James M. Daly 10,000 10 years 86.32 Total 85,000 24,972 2019 ESOPs Term Exercise price Exercised Peter Verhaeghe 10,000 10 years 135.75 David L Lacey 10,000 10 years 135.75 Werner Lanthaler 10,000 10 years 135.75 11.38 4,444 Pamela Klein 10,000 10 years 135.75 Don Debethizy 10,000 10 years 135.75 A.A. Rosenberg 10,000 10 years 135.75 James M. Daly 10,000 10 years 135.75 Total 70,000 4,444 The table below shows the stock options held at the start of the year ended December 31, 2019 and the stock options granted to the non‑executive directors which have vested during the year ended December 31, 2019, as well as the stock options to vest in the years ending December 31, 2020, December 31, 2021 and December 31, 2022 (in number of stock options), and the respective exercise price of such stock options: Total Total Options Options Options options Options Options options Options Options to to to held on granted exercised held on vested vested vest vest vest January 1, in in December 31, until Exercise in Exercise in Exercise in Exercise in Exercise Name 2019 2019 2019 2019 2018 price 2019 price 2020 price 2021 price 2022 price Peter Verhaeghe 44,585 10,000 54,585 11,626 € 2.44 7,959 € 3.95 5,000 € 7.17 8,333 € 11.38 1,667 € 11.38 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 David L. Lacey 54,443 10,000 64,443 6,643 € 2.44 12,800 € 7.17 8,333 € 11.38 1,667 € 11.38 5,000 € 21.17 5,000 € 21.17 5,000 € 21.17 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 Werner Lanthaler 14,444 10,000 (4,444) 20,000 — € 2.44 — € 7.17 — € 11.38 — € 11.38 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 J. Donald deBethizy 35,000 10,000 45,000 15,000 € 11.44 8,333 € 11.38 1,667 € 11.38 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 Pamela Klein 35,000 10,000 45,000 15,000 € 11.44 8,333 € 11.38 1,667 € 11.38 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 A.A. Rosenberg 25,000 10,000 35,000 10,000 € 14.13 5,000 € 14.13 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 James M. Daly 25,000 10,000 35,000 7,500 € 80.82 5,000 € 80.82 2,500 € 80.82 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 The table below shows the remaining term of the stock options held by the non‑executive directors on December 31, 2019. Remaining term on Number of December 31, 2019 Name stock options (rounded up) Peter K.M. Verhaeghe 3,650 0.5 years 2,340 1.0 years 5,560 3.5 years 3,181 4.0 years 9,854 5.0 years 10,000 6.5 years 10,000 9.0 years 10,000 10.0 years David L. Lacey 3,180 3.5 years 1,818 4.0 years 14,445 5.0 years 10,000 6.5 years 15,000 8.0 years 10,000 9.0 years 10,000 10.0 years Werner Lanthaler 10,000 9.0 years 10,000 10.0 years J. Donald deBethizy 15,000 5.5 years 10,000 6.5 years 10,000 9.0 years 10,000 10.0 years Pamela Klein 15,000 5.5 years 10,000 6.5 years 10,000 9.0 years 10,000 10.0 years A.A. Rosenberg 15,000 7.0 years 10,000 9.0 years 10,000 10.0 years James M. Daly 15,000 8.5 years 10,000 9.0 years 10,000 10.0 years Stock options are granted to the non-executive directors by the Board based on the recommendation of the Remuneration and Nomination Committee, and the option allocation scheme established by the board pursuant to the argenx Employee Stock Option Plan.

Contingencies

Contingencies	12 Months Ended
	Dec. 31, 2019
Contingencies
Contingencies	29. Contingencies The Company is currently not facing any outstanding claims or litigations that may have a significant adverse impact on the Company’s financial position. As described in note 18, the Company has received several types of government grants which are granted subject to a certain number of conditions that need to be met at grant date and in the future. The Company recognizes grant income from Belgian and Flemish grant bodies when all contractual conditions are met. These government institutions may however subsequently perform an audit which may result in a (partial) claw back of the grant. The Company deems that the claw back risk is remote in view of the continuous monitoring of the contractual conditions. The Company has fulfilled all existing conditions relating to the recognition of its grant income. Contracts with these grant bodies also typically include clauses that define the need for future validation of the project results after completion of the initial grant term during which the subsidized expenses or investments have been incurred and for which the grant was earned. Should this validation not occur or be deemed inadequate, the grant bodies have the right to reclaim funds previously granted. As described in note 13, in 2019, the Company granted a total of 1,365,172 stock options to certain of its employees, Board members and consultants. As part of the grant of these stock options, the Company has undertaken to compensate Belgian taxes that are paid upon the grant of these stock options if and when at the end of the exercise period, the stock price would be lower than the exercise price, as increased with these taxes. The Company has applied for a tax ruling on this subject that would cover the stock option grants as from June 28, 2018. The exposure that the Company could face at the end of the exercise period for the stock options granted in 2018 and 2019 ranges from €7.6 million to €8.6 million.

Commitments

Commitments	12 Months Ended
	Dec. 31, 2019
Commitments
Commitments	30. Commitments At balance sheet date, there were no commitments signed for the acquisition of property, plant and equipment. In February 2019, the Company entered into a global collaboration and license agreement with Halozyme Therapeutics, Inc. Under the terms of the agreement, the Company will pay $10.0 million per target for future target nominations and potential future payments of up to $160.0 million per selected target subject to achievement of specified development, regulatory and sales-based milestones and up to $40.0 million subject to the achievement of additional, specified sales-based milestones. This amount represents the maximum amount that would be paid if all milestones would be achieved but excludes variable royalty payments based on unit sales. For the year ended December 31, 2019, the Company exercised the option to nominate an additional target (triggering a $10 million development milestone payment) and initiated a Phase 1 clinical trial using Halozyme's proprietary ENHANZE® drug delivery technology (triggering a $5 million development milestone payment). The Company’s manufacturing commitments with its drug substance manufacturing contractor Lonza relate to the ongoing execution of the BLA services for efgartigimod and the ongoing manufacturing activities related to the start-up of Lonza Singapore as a potential future commercial manufacturing site. In December 2018, the Company signed its first commercial supply agreement with Lonza related to the reservation of commercial drug substance supply capacity for efgartigimod. The total commitment under this commercial supply agreement amounts to a minimum commitment of £25.3 million over a period of five years starting from 2020. In the aggregate, the Company has outstanding commitments for efgartigimod of approximately €53.4 million. In addition, the Company also has contractual obligations for cusatuzumab of approximately €34.4 million and for ARGX-117 of approximately €3.6 million.

Audit fees

Audit fees	12 Months Ended
	Dec. 31, 2019
Audit fees
Audit fees	31. Audit fees The following auditors’ fees were expensed in the income statement: Year Ended December 31, Fees 2019 2018 2017 in thousands of € Audit fees (1) € 730 € 648 € 179 Audit-related fees 159 143 724 Tax and other services (2) — — — Total € 889 € 791 € 903 (1) Audit services performed by Deloitte Accountants B.V. as the external auditor referred to in Section 1 of the Dutch Accounting Firms Oversight Act (Wta) as well as by the Deloitte network. (2) Tax and other services performed by the Deloitte network.

Overview of consolidation scope

Overview of consolidation scope	12 Months Ended
	Dec. 31, 2019
Overview of consolidation scope
Overview of consolidation scope	32. Overview of consolidation scope The parent company argenx SE is domiciled in the Netherlands. The Company, argenx SE, has one subsidiary, argenx BV, based in Belgium. argenx BV has two subsidiary, argenx US, Inc., based in the United States of America and argenx Japan KK, based in Japan. Details of the Company’s consolidated entities at the end of the reporting period are as follows: Name Registration number Country Participation Main activity argenx SE COC 24435214 The Netherlands 100.00 % Holding company argenx BV Belgium 100.00 % Biotechnical research on drugs and pharma processes argenx US, Inc. 36-4880497 USA 100.00 % Pharmaceuticals and pharmacy supplies merchant wholesalers argenx Japan KK 0104-01-145183 Japan 100.00 % Pharmaceuticals and pharmacy supplies merchant wholesalers

Events after the balance sheet

Events after the balance sheet date	12 Months Ended
	Dec. 31, 2019
Events after the balance sheet date
Events after the balance sheet date	33. Events after the balance sheet date The recent outbreak of COVID-19 originated in Wuhan, China, in December 2019 and has since spread to multiple countries, including the United States and several European countries. On March 11, 2020, the World Health Organization declared the outbreak a pandemic. The spread of COVID-19 has impacted the global economy and may impact our operations, including the potential interruption of our clinical trial activities and our supply chain. For example, the COVID-19 outbreak may delay enrollment in our clinical trials due to prioritization of hospital resources toward the outbreak, and some patients may be unwilling to enroll in our trials or be unable to comply with clinical trial protocols if quarantines impede patient movement or interrupt healthcare services, which would delay our ability to conduct clinical trials or release clinical trial results. The spread of an infectious disease, including COVID-19, may also result in the inability of our suppliers to deliver clinical drug supplies on a timely basis or at all. In addition, hospitals may reduce staffing and reduce or postpone certain treatments in response to the spread of an infectious disease. Such events may result in a period of business disruption, and in reduced operations, or doctors and medical providers may be unwilling to participate in our clinical trials, any of which could materially affect our business, financial condition and results of operations. The extent to which the recent global COVID-19 pandemic impacts our business will depend on future developments, which are highly uncertain and cannot be predicted, including new information that may emerge concerning the severity of COVID-19 and the actions to contain or treat its impact, among others. Any significant infectious disease outbreak, including the COVID-19 pandemic, could result in a widespread health crisis that could adversely affect the economies and financial markets worldwide, resulting in an economic downturn that could impact our business, financial condition and results of operations, including our ability to obtain additional funding, if needed. The Company is proactively executing risk mitigation strategies to attenuate the impact of COVID-19.

Significant accounting polici_2

Significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2019
Significant accounting policies
Statement of compliance and basis of preparation	2.1 Statement of compliance and basis of preparation The consolidated financial statements are prepared in accordance with the International Financial Reporting Standards (IFRS), issued by the International Accounting Standards Board (IASB) and the interpretations issued by the IASB’s International Financial Reporting Interpretation Committee. The consolidated financial statements provide a general overview of the Company’s activities and the results achieved. They present fairly the entity’s financial position, its financial performance and cash flows, on a going concern basis. The accounting policies described in Note 2 to our consolidated financial statements have been applied in preparing the consolidated financial statements as of and for the year ended December 31, 2019 and for the comparative information as of and for the years ended December 31, 2018 and 2017. The preparation of consolidated financial statements in conformity with IFRS, issued by the IASB, requires the use of certain critical accounting estimates. It also requires management to exercise its judgment in the process of applying the Company’s accounting policies. The areas involving a higher degree of judgment or complexity, or areas where assumptions and estimates are significant to the consolidated financial statements are disclosed in Note 3. The significant accounting policies applied in the preparation of the above consolidated financial statements are set out below. All amounts are presented in thousands of euro, unless otherwise indicated, rounded to the nearest € ‘000. The consolidated financial statements have been approved for issue by the Company’s Board of Directors (the Board) on March 31, 2020.
Basis of consolidation	2.2 Basis of consolidation The consolidated financial statements include the financial statements of the Company and entities controlled by the Company (its subsidiaries). Control is achieved when the Company: · has power over the investee; · is exposed, or has rights, to variable returns from its involvement with the investee; and · has the ability to use its power to affect its returns. The Company reassesses whether or not it controls an investee if facts and circumstances indicate that there are changes to one or more of the three elements of control listed above. Consolidation of a subsidiary begins when the Company obtains control over the subsidiary and ceases when the Company loses control of the subsidiary. Income and expenses of subsidiaries acquired or disposed of during the year are included in the consolidated statement of profit and loss and other comprehensive income from the effective date of acquisition and up to the effective date of disposal, as appropriate. When necessary, adjustments are made to the financial statements of subsidiaries to bring their accounting policies into line with those used by other members of the Group. All inter-company transactions and unrealized gains on transactions between group companies are eliminated. Unrealised losses are also eliminated unless the transaction provides evidence of an impairment of the transferred asset. Accounting policies of subsidiaries have been changed where necessary to ensure consistency with the policies adopted by the Group.
Foreign currency transactions	2.3 Foreign currency transactions Functional and presentation currency The consolidated financial statements are presented in euro (€), which is the Company’s presentation currency and the Company’s functional currency. Transactions and balances Transactions in foreign currencies are translated at the exchange rate ruling at the date of the transaction. Monetary assets and liabilities denominated in foreign currencies are translated at the exchange rate ruling at the reporting date. Foreign exchange differences arising on translation are recognized in the statement of profit and loss and other comprehensive income. Non‑monetary assets and liabilities denominated in foreign currencies are translated at the foreign exchange rate ruling at the date of the transaction. Financial statements of foreign entities For foreign entities using a different functional currency than the euro: · assets and liabilities for each balance sheet presented are translated at the closing rate at the date of that statement of financial position. · income and expenses for each statement presenting profit or loss and other comprehensive income are translated at average exchange rates (unless this average is not a reasonable approximation of the cumulative effect of the rates prevailing on the transaction dates, in which case income and expenses are translated at the rate on the dates of the transactions). · all resulting exchange differences are recognised in other comprehensive income.
Intangible assets	2.4 Intangible assets 2.4.1 Internally generated intangible assets Expenditure on research activities is recognized as an expense in the period in which it is incurred. An internally‑generated intangible asset arising from development (or from the development phase of an internal project) is recognized if, and only if, all of the following have been demonstrated: · the technical feasibility of completing the intangible asset so that it will be available for use or sale; · the intention to complete the intangible asset and use or sell it; · the ability to use or sell the intangible asset; · how the intangible asset will generate probable future economic benefits; · the availability of adequate technical, financial and other resources to complete the development and to use or sell the intangible asset; and · the ability to measure reliably the expenditure attributable to the intangible asset during its development. The amount initially recognized for internally‑generated intangible assets is the sum of the expenditure incurred from the date when the intangible asset first meets the recognition criteria listed above. Where no internally‑generated intangible asset can be recognized, development expenditures are recognized in the statement of profit and loss and other comprehensive income in the period in which they are incurred. Due to uncertainties inherent to the development and registration with the relevant healthcare authorities of its products, the Company estimates that the conditions for capitalization are not met until the regulatory procedures required by such healthcare authorities have been finalized. The Company currently does not own products that have been approved by the relevant healthcare authorities. Subsequent to initial recognition, internally‑generated intangible assets are reported at cost less accumulated amortization and accumulated impairment losses, on the same basis as intangible assets that are acquired separately. 2.4.2 Intangible assets acquired separately Intangible assets with finite useful lives that are acquired separately are carried at cost less accumulated amortization and accumulated impairment losses. Amortization is recognized on a straight‑line basis over their estimated useful lives which are disclosed in note 4. The estimated useful life and amortization method are reviewed at the end of each reporting period, with the effect of any changes in estimate being accounted for on a prospective basis. Intangible assets with indefinite useful lives that are acquired separately are carried at cost less accumulated impairment losses. Payments for acquired in-process research and development projects obtained through in-licensing arrangements, business combinations and separate asset purchases are capitalized as intangible assets provided that they are separately identifiable, controlled by the Company and expected to provide future economic benefits. As the probability criterion in IAS 38 is always considered to be satisfied for separately acquired research and development assets and the amount of the payments is determinable, upfront and milestone payments to third parties for pharmaceutical products or compounds for which regulatory marketing approval has not yet been obtained are recognized as intangible assets, and amortized on a straight line basis over their useful lives beginning when the underlying drug candidate is approved and launched commercially, or expensed immediately if development of the drug candidate is abandoned. 2.4.3 Derecognition of intangible assets An intangible asset is derecognized either on disposal or when no future economic benefits are expected from its use. Gains or losses arising from derecognition of an intangible asset, measured as the difference between the net disposal proceeds and the carrying amount of the asset, are recognized in profit or loss when the asset is derecognized.
Property, plant and equipment	2.5 Property, plant and equipment Items of property, plant and equipment held for use in the production or supply of goods or services, or for administrative purposes, are stated in the statement of financial position at their cost, less accumulated depreciation and accumulated impairment losses. The cost comprises the initial purchase price plus other direct purchase costs (such as non‑refundable tax and transport). Depreciation is recognized as from acquisition date onwards (unless asset is not ready for use) so as to write off the cost or valuation of assets (other than freehold land and properties under construction) less their residual values over their useful lives, using the straight‑line method. The estimated useful lives, residual values and depreciation method are reviewed at the end of each reporting period, with the effect of any changes in estimate accounted for on a prospective basis. Unless revised due to specific changes in the estimated useful life, annual depreciation rates are as follows: · Office and lab equipment: 3–5 years · IT equipment: 3 years An item of property, plant and equipment is derecognized upon disposal or when no future economic benefits are expected to arise from the continued use of the asset. Any gain or loss arising on the disposal or retirement of an item of property, plant and equipment is determined as the difference between the sales proceeds and the carrying amount of the asset and is recognized in profit or loss.
Leases	2.6 Leases As explained in note 2.22 below, the Company has changed its accounting policy for leases where the Company is the lessee. Until December 31, 2018, leases of property, plant and equipment where the Company, as lessee, had substantially all the risks and rewards of ownership were classified as finance leases. Finance leases were capitalised at the lease’s inception at the fair value of the leased property or, if lower, the present value of the minimum lease payments. The corresponding rental obligations, net of finance charges, were included in other short-term and long-term payables. Each lease payment was allocated between the liability and finance cost. The finance cost was charged to the profit or loss over the lease period so as to produce a constant periodic rate of interest on the remaining balance of the liability for each period. The property, plant and equipment acquired under finance leases was depreciated over the asset’s useful life or over the shorter of the asset’s useful life and the lease term if there is no reasonable certainty that the Company will obtain ownership at the end of the lease term. Leases in which a significant portion of the risks and rewards of ownership were not transferred to the Company as lessee were classified as operating leases. Operating lease payments were recognized as an expense on a straight‑line basis over the lease term, except where another systematic basis was more representative of the time pattern in which economic benefits from the leased asset are consumed. As from January 1, 2019, the Company assesses whether a contract is or contains a lease, at inception of the contract. The Company recognises a right-of-use asset and a corresponding lease liability with respect to all lease arrangements in which it is the lessee, except for short-term leases (defined as leases with a lease term of 12 months or less) and leases of low value assets. For these leases, the Company recognises the lease payments as an operating expense on a straight-line basis over the term of the lease unless another systematic basis is more representative of the time pattern in which economic benefits from the leased assets are consumed. The lease liability is initially measured at the present value of the lease payments that are not paid at the commencement date, discounted by using the rate implicit in the lease. If this rate cannot be readily determined, the lessee uses its incremental borrowing rate. The lease liability is subsequently measured by increasing the carrying amount to reflect interest on the lease liability (using the effective interest method) and by reducing the carrying amount to reflect the lease payments made. The lease liability is presented as a separate line in the consolidated statement of financial position. The right-of-use assets comprise the initial measurement of the corresponding lease liability, lease payments made at or before the commencement day, less any lease incentives received and any initial direct costs. They are subsequently measured at cost less accumulated depreciation and impairment losses. Right-of-use assets are depreciated over the shorter period of lease term and useful life of the underlying asset. If a lease transfers ownership of the underlying asset or the cost of the right-of-use asset reflects that the Company expects to exercise a purchase option, the related right-of-use asset is depreciated over the useful life of the underlying asset. The right-of-use assets are presented in the statement of financial position under the caption “Property, plant and equipment”.
Impairment of assets	2.7 Impairment of assets At the end of each reporting period, the Company reviews the carrying amounts of its tangible and intangible assets to determine whether there is any indication that those assets have suffered an impairment loss. If any such indication exists, the recoverable amount of the asset is estimated in order to determine the extent of the impairment loss (if any). Where it is not possible to estimate the recoverable amount of an individual asset, the Company estimates the recoverable amount of the cash‑generating unit to which the asset belongs. Intangible assets with indefinite useful lives and intangible assets not yet available for use are tested for impairment at least annually, and whenever there is an indication that the asset may be impaired. Recoverable amount is the higher of fair value less costs to sell and value in use. In assessing value in use, the estimated future cash flows are discounted to their present value using a pre‑tax discount rate that reflects current market assessments of the time value of money and the risks specific to the asset for which the estimates of future cash flows have not been adjusted. If the recoverable amount of an asset (or cash‑generating unit) is estimated to be less than its carrying amount, the carrying amount of the asset (or cash‑generating unit) is reduced to its recoverable amount. An impairment loss is recognized immediately in profit or loss. Where an impairment loss subsequently reverses, the carrying amount of the asset (or a cash‑generating unit) is increased to the revised estimate of its recoverable amount, but so that the increased carrying amount does not exceed the carrying amount that would have been determined had no impairment loss been recognized for the asset (or cash‑generating unit) in prior years. A reversal of an impairment loss is recognized immediately in profit or loss.
Financial assets: investments	2.8 Financial assets: investments (i) Classification The Company classifies its financial assets in the following measurement categories: those to be measured subsequently at fair value through profit or loss (FVTPL) and those to be measured at amortized cost. The classification depends on the Company’s business model for managing the financial assets and the contractual terms of the cash flows. Regular purchases and sales of financial assets are recognized on the trade date – the date on which the Company commits to purchase or sell the asset. Financial assets are derecognized when the rights to receive cash flows from the investments have expired or have been transferred and the Company has transferred substantially all risks and rewards of ownership. For assets measured at fair value, gains and losses will be recorded in profit or loss. (ii) Measurement At initial recognition, the Company measures a financial asset at its fair value plus, in case of a financial asset not at FVTPL, transaction costs that are directly attributable to the acquisition of the financial asset. Transaction costs of financial assets carried at FVTPL are expensed in profit or loss. The Company subsequently measures all equity investments at fair value. Dividends from such investments continue to be recognized in profit or loss as financial income when the Company’s right to receive payments is established. Changes in the fair value of financial assets at FVPL are recognized in financial income/expenses in the statement of profit or loss. The fair value of listed investments is based on current market prices. If the market for a financial asset is not active (and for unlisted securities), the Company establishes fair value by using valuation techniques.
Trade and other receivables	2.9 Trade and other receivables Trade receivables are recognised initially at the amount of consideration that is unconditional. The Company holds the trade receivables with the objective to collect the contractual cash flows and therefore measures them subsequently at amortised cost using the effective interest method. Unless the impact of discounting is material, the nominal value is recognized. Trade receivables are recognized initially at their transaction price and are subsequently measured at amortized cost using the effective interest rate method, less provision for expected credit losses. For determining the expected credit losses, the Company applies the simplified approach permitted by IFRS 9, which requires lifetime losses to be recognized from initial recognition of the receivables.
Research and development incentive receivables	2.10 Research and development incentive receivables Since the Company carries out extensive research and development activities, it benefits from a research and development incentive tax scheme in Belgium under which the research and development incentives can be refunded after five years if not offset against future income tax expense. These research and development incentives generally aim to partly reimburse expenditures incurred in our research and development efforts and are credited to the statement of profit or loss under the line “Other operating income” when the relevant expenditure has been incurred and there is a reasonable assurance that the research and development incentives are receivable.
Cash and cash equivalents	2.11 Cash and cash equivalents Cash and cash equivalents includes cash in hand, deposits held at call with banks and other short term highly liquid investments with original maturities of three months or less and with an insignificant risk of changes in value. Bank overdrafts, if any, are shown within borrowings in current liabilities on the statement of financial position. Cash balances that are not available for use by the Company are presented as “restricted cash” in the statement of financial position. For the purpose of the statements of cash flows, cash and cash equivalents includes cash on hand and deposits held at call or short term maturity with banks (three months or less with insignificant risk of changes in value).
Shareholder's equity	2.12 Shareholder’s equity An equity instrument is any contract that evidences a residual interest in the assets of an entity after deducting all of its liabilities. Equity instruments issued by the Company are recognized at the proceeds received, net of direct issue costs. The Company has never distributed any dividends to its shareholders. As of December 31, 2019, no profits were available for distribution.
Trade and other payables	2.13 Trade and other payables Payables after and within one year are measured at amortized cost, i.e., at the net present value of the payable amount. Unless the impact of discounting is material, the nominal value is recognized.
Provisions	2.14 Provisions Provisions are recognized when the Company has a present obligation (legal or constructive) as a result of a past event, it is probable that the Company will be required to settle the obligation, and a reliable estimate can be made of the amount of the obligation. The amount recognized as a provision is the best estimate of the consideration required to settle the present obligation at the end of the reporting period, taking into account the risks and uncertainties surrounding the obligation. When a provision is measured using the cash flows estimated to settle the present obligation, its carrying amount is the present value of those cash flows (where the effect of the time value of money is material). When some or all of the economic benefits required to settle a provision are expected to be recovered from a third party, a receivable is recognized as an asset if it is reasonably certain that reimbursement will be received and the amount of the receivable can be measured reliably.
Retirement benefits	2.15 Retirement benefits The Company offers a post‑employment, death, disability and healthcare benefit scheme. All employees have access to these schemes. The death, disability and healthcare benefits granted to employees of the Company are covered by an external insurance company, where premiums are paid annually and charged to the income statement as they were incurred. The post‑employment pension plan granted to employees of the Company is a defined contribution plan under Belgian Law. Under defined contribution plans, the Company pays contributions based on salaries to organizations responsible for paying out pensions and social security benefits, in accordance with the laws and agreements applicable in each country. The Belgian defined contribution pension plans are by law subject to minimum guaranteed rates of return, historically 3.25% on employer contributions and 3.75% on employee contributions. These rates have been modified by the law of December 18, 2015 and effective for contribution paid as from 2016 to a new variable minimum return based on the OLO (‘Obligation Lineaire Obligaties’—Belgian Government Bond) rates, with a minimum of 1.75% and a maximum of 3.75%. Hence, from 2016 onwards, these plans are accounted for as defined benefit plans (see note 14). The liability recognized in the balance sheet is the present value of the defined benefit obligation less the fair value of plan assets. An independent actuary calculates the defined benefit obligation based on factors such as age, years of service and compensation (projected unit credit method). The present value of the defined benefit obligation is determined by discounting the estimated future cash outflows using interest rates of high‑quality corporate bonds denominated in the currency in which the benefits will be paid and with terms to maturity that approximate the term when the related liability is due. Current service costs are recognized in personnel expenses, which are included in Research and development expenses and in Selling, general and administrative expenses, and reflect the increase in the defined benefit obligation resulting from employee service in the current year. Past service costs are recognized immediately in personnel expenses. The net interest expense on the defined benefit liability is determined by applying the discount rate used to measure the defined benefit obligation at the beginning of the year to the then net defined benefit liability. Net interest expense is recognized in personnel expenses. Remeasurement gains and losses of the defined benefit obligation arising from experience adjustments and changes in actuarial assumptions are recognized immediately in other comprehensive income.
Research and development cost accruals	Research and development cost accruals The Company recognizes costs of €44.0 million, as specified in note 15 to the financial statements, incurred for clinical trial activities and manufacturing of drug products, as research and development expenses based on an evaluation of its vendors’ progress toward completion of specific tasks. Payment timing may differ significantly from the period in which the costs are recognized as expense, resulting in clinical trial accruals recognized within Trade and other payables in the statement of financial position. Quantification of the research progress and the translation of the progress to these accruals requires judgment, because the progress is not directly observable. In estimating the vendors’ progress toward completion of specific tasks, the Company therefore uses data such as patient enrollment, clinical site activations and vendor information of actual costs incurred. This data is obtained through reports from or discussions with Company personnel and outside service providers as to the progress or state of completion of trials, or the completion of services. Costs are expensed over the service period the services are provided. Costs for services provided that have not yet been paid are recognized as accruals. Research and development cost accruals directly impact the revenue recognized, given the Company records revenue based on the percentage of completion method.
Short-term employee benefits	2.16 Short‑term employee benefits Short‑term employee benefits include payables and accruals for salaries and bonuses to be paid to the employees of the Company. They are recognized as expenses for the period in which employees perform the corresponding services.
Share-based payments	2.17 Share‑based payments Equity‑settled share‑based payments to employees and others providing similar services are measured at the fair value of the equity instruments at the grant date. Details regarding the determination of the fair value of equity‑settled share‑based transactions are set out in note 13. The fair value determined at the grant date of the equity‑settled share‑based payments is expensed on a straight‑line basis over the vesting period, based on the Company’s estimate of equity instruments that will eventually vest, with a corresponding increase in equity. At the end of each reporting period, the Company revises its estimate of the number of equity instruments expected to vest. The impact of the revision of the original estimates, if any, is recognized in profit or loss such that the cumulative expense reflects the revised estimate, with a corresponding adjustment to the equity‑settled share‑based payment reserve. Where the terms of equity‑settled share‑based payments are modified, the minimum expense recognized is the expense that would have been recognized if the terms had not been modified. An additional expense is recognized for any modification that increases the total fair value of the share‑based payments, or is otherwise beneficial to the employee as measured at the date of modification.
Deferred revenue	2.18 Deferred revenue Current and non-current deferred revenue relates to cash received from commercial partnerships prior to completion of the earnings process. These payments are recognized as revenue over the estimated duration of the Company’s involvement in the research and development programs provided for under the terms of the agreements. IFRS 15 uses the term ‘contract liability’ to describe what might more commonly be known as ‘deferred revenue’, however IFRS 15 does not prohibit an entity from using alternative descriptions in the statement of financial position. The Company will continue to report its contract liabilities under the term ‘deferred revenue.
Income taxes	2.19 Income taxes Income tax expense represents the sum of the tax currently payable and deferred tax. The tax currently payable is based on taxable profit for the year. Taxable profit differs from profit as reported in the statement of profit and loss and other comprehensive income because of items of income or expense that are taxable or deductible in other years and items that are never taxable or deductible. The Company’s liability for current tax is calculated using tax rates that have been enacted or substantively enacted by the end of the reporting period. Deferred tax is recognized on temporary differences between the carrying amounts of assets and liabilities in the consolidated financial statements and the corresponding tax basis used in the computation of taxable profit (e.g. differences between carrying amounts under IFRS and the statutory tax basis). Deferred tax liabilities are generally recognized for all taxable temporary differences. Deferred tax assets are generally recognized for all deductible temporary differences to the extent that it is probable that taxable profits will be available against which those deductible temporary differences can be utilized. Such deferred tax assets and liabilities are not recognized if the temporary difference arises from goodwill or from the initial recognition (other than in a business combination) of other assets and liabilities in a transaction that affects neither the taxable profit nor the accounting profit. The carrying amount of deferred tax assets is reviewed at the end of each reporting period and reduced to the extent that it is no longer probable that sufficient taxable profits will be available to allow all or part of the asset to be recovered. Deferred tax assets and liabilities are measured at the tax rates that are expected to apply in the period in which the liability is settled or the asset realized, based on tax rates (and tax laws) that have been enacted or substantially enacted by the end of the reporting period. The measurement of deferred tax liabilities and assets reflects the tax consequences that would follow from the manner in which the Company expects, at the end of the reporting period, to recover or settle the carrying amount of its assets and liabilities. Deferred tax assets and deferred tax liabilities are offset if there is a legally enforceable right to offset current tax assets and liabilities and if they relate to income taxes imposed by the same authority on the same taxable entity or in different tax entities that intend to settle current tax assets and liabilities on a net basis or their tax assets and liabilities will be realized simultaneously.
Revenue and other operating income recognition	2.20 Revenue and other operating income recognition Collaborations The Company adopted IFRS 15 on January 1, 2018. The Company elected the modified retrospective approach for the transition, which foresees that prior period figures remain as reported under the previous standard IAS 18, and the cumulative effect of applying IFRS 15 is recognized as an adjustment to the opening balance of equity as at the date of initial application (i.e., the beginning of the year 2018). In previous reporting periods, milestone payments were recognized under IAS 18 based upon the achievement of the milestone event, whereas under IFRS 15, the milestone payment is linked to a single performance obligation over the estimated service period. The revenue recognition of the upfront payments was not impacted by the transition from IAS 18 to IFRS 15. The cumulative effect of adopting IFRS 15 to the consolidated statement of financial position as of January 1, 2018 was as follows: (in thousands of €) Balance at December 31, 2017 Adjustments due to adoption IFRS 15 Balance at January 1, 2018 Assets Prepaid expenses € 2,338 € (255) € 2,083 Liabilities Deferred revenue — non-current € 1,435 € 378 € 1,813 Deferred revenue — current 8,635 2,272 10,907 Equity Accumulated losses € (100,568) € (2,395) € (102,962) The Company generates revenue from collaborations and strategic alliances. The Company applies a five-step model to determine when, how and at what amount revenue is to be recognized depending on whether certain criteria are met. 1. Identify the contracts In our current arrangements, the Company is licensing its Intellectual Property, providing research and development services and in the future, selling its products to collaborative partner entities. Revenue is generated through these arrangements via upfront payments, milestone payments based on development criteria, research and development service fees on an agreed full-time equivalent (FTE) basis and future sales based milestones and sales based royalties. 2. Identify performance obligations The Company has assessed that there is one single performance obligation in our material ongoing license and collaboration arrangements, being the transfer of a license combined with performance of research and development services. This is because we consider that the performance obligations cannot be distinct in the context of the contract as the license has no stand-alone value without the Company being further involved in the research and development collaboration and that there is interdependence between the license and the research and development services to be provided. We estimate that the Company’s activities during the collaboration are going to significantly add to Intellectual Property and thereby the value of the programs. 3. Determine the transaction price We have analyzed the transaction prices of our material ongoing license and collaboration arrangements currently composed of upfront payments, milestone payments and research and development service fees being delivered. Any variable consideration, such as development milestone payments that are promised in exchange for development services or the license of IP, is only included in the transaction price as from the moment the achievement of the related milestone event is highly probable (usually at the time of achievement of the milestone event). At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such milestones and any related constraint, and, if necessary, adjusts the estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and earnings in the period of adjustment. The Company’s collaborators may be required to pay the Company sales-based milestone payments or royalties on future sales of commercial products. The Company recognizes revenues related to sales-based milestone and royalty payments upon the later to occur of (i) achievement of the collaborator’s underlying sales or (ii) satisfaction of any performance obligation(s) related to these sales, in each case assuming the license to the Company’s intellectual property is deemed to be the predominant item to which the sales-based milestones and/or royalties relate. 4. Allocate the transaction price In principle, an entity shall allocate the transaction price to each performance obligation identified in the contract on a relative stand-alone selling price basis. However, the transaction price of certain of our arrangements is allocated to a single performance obligation since the transfer of a license is considered to be combined with performance of research and development services. Therefore, research and development milestone payments are variable considerations that are entirely allocated to the single performance obligation. 5. Recognize revenue Revenue from certain arrangements is recognized over time as the Company satisfies a single performance obligation. Our collaborative partner entities simultaneously receive the benefits provided by the Company’s performance as the Company performs. The Company recognizes upfront payments and milestone payments, allocated to a single performance obligation over the estimated service period based on a pattern that reflects the transfer of the services. The revenues recognized reflect the level of service each period. In this case, the Company would use an input model that considers estimates of the percentage of total research and development service costs that are completed each period compared to the total estimated services costs (percentage of completion method). Research and development service fees are recognized as revenue when costs are incurred and agreed by the parties as the Company is acting as a principal in the scope of its stake of the research and development activities of its ongoing license and collaboration agreements. Grants, research and development incentives and payroll tax rebates Because it carries out extensive research and development activities, the Company benefits from various grants, research and development incentives and payroll tax rebates from certain governmental agencies. These grants, research and development incentives and payroll tax rebates generally aim to partly reimburse approved expenditures incurred in research and development efforts of the Company and are credited to the statement of profit and loss and other comprehensive income, under other operating income, when the relevant expenditure has been incurred and there is reasonable assurance that the grants or research and development incentives are receivable.
Earnings per share	2.21 Earnings per share Basic net profit / (loss) per share is computed based on the weighted average number of ordinary shares outstanding during the period, excluding treasury shares. Diluted net profit / (loss) per share is computed based on the weighted‑average number of ordinary shares outstanding including the dilutive effect of options. Options should be treated as dilutive, when and only when their conversion to ordinary shares would decrease net profit per share from continuing operations.
Adoption of new and revised standards	2.22 Adoption of new and revised standards New ac The following new standard is mandatory for the first time for the financial year beginning on or after January 1, 2019: ■ IFRS 16, ‘Leases’ (effective for fiscal years beginning on or after January 1, 2019). This standard replaces the current guidance in IAS 17 and is a far reaching change in accounting by lessees in particular. Under IAS 17, lessees were required to make a distinction between a finance lease (on balance sheet) and an operating lease (off balance sheet). IFRS 16 requires lessees to recognise a lease liability reflecting future lease payments and a ‘right-of-use asset’ for virtually all lease contracts. For lessors, the accounting stays almost the same. However, as the IASB has updated the guidance on the definition of a lease (as well as the guidance on the combination and separation of contracts), lessors will also be affected by the new standard. Under IFRS 16, a contract is, or contains, a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company has adopted IFRS 16 on January 1, 2019. The Company elected to apply the modified retrospective approach for the transition, which foresees that prior period figures remain as reported under the previous standard IAS 17, and the cumulative effect of applying IFRS 16 is recognized as an adjustment to the opening balance of equity as of the date of initial application (i.e., the beginning of the year 2019). On adoption of IFRS 16, the Company recognized lease liabilities in relation to leases which had previously been classified as ‘operating leases’ under IAS 17. These liabilities were measured at the present value of the remaining lease payments and discounted using the Company’s incremental borrowing rate as of January 1, 2019. The Company’s weighted average incremental borrowing rate applied to these lease liabilities on January 1, 2019 was 1.32%. The differences between our total operating lease commitments as reported in note 5.7 of our consolidated financial statements of December 31, 2018 and the total lease liabilities recognized in our statement of financial position as at January 1, 2019 are summarized below: (in thousands of €) Operating lease commitments disclosed as at December 31, 2018 € 3,004 Less: discounting effect using the lessee's incremental borrowing rate of the date of initial application € (126) Less: short-term leases recognized on a straight-line basis as expense € (88) Lease liability recognized as at January 1, 2019 € 2,790 of which are: Current lease liabilities € 1,078 Non-current lease liabilities € 1,712 The cumulative effect of adopting IFRS 16 to the consolidated statement of financial position as of January 1, 2019 is as follows: (in thousands of €) Property, plant and equipment (right-of-use assets) € 2,790 Effect on total assets € 2,790 Lease liabilities (current and non-current) € 2,790 Effect on total equity and liabilities € 2,790 The adoption of IFRS 16 does not have a significant impact on the metrics used to measure financial performance. In applying IFRS 16 for the first time, the Company has used the following practical expedients permitted by the standard: · the use of a single discount rate to a portfolio of leases with reasonably similar characteristics; · reliance on previous assessments on whether leases are onerous; · the accounting for operating leases with a remaining lease term of less than 12 months as at January 1, 2019 as short-term leases; and · the use of hindsight in determining the lease term where the contract contains options to extend or terminate the lease. The Company has also elected not to reassess whether a contract is, or contains, a lease at the date of initial application. Instead, for contracts entered into before the transition date, the Company relied on its assessment made applying IAS 17 and IFRIC 4 Determining whether an Arrangement contains a Lease . ■ Other new standards and amendments to standards that are mandatory for the first time for the financial year beginning on or after January 1, 2019 had no material impact on our consolidated financial statements. New accounting policies and disclosures effective in 2020 or later The following new standards and amendments to standards have been issued, but are not mandatory for the first time for the financial year beginning January 1, 2019 and have been endorsed by the European Union. ■ Amendments to References to the Conceptual Framework in IFRS Standards (effective 1 January 2020). The revised Conceptual Framework includes a new chapter on measurement; guidance on reporting financial performance; improved definitions and guidance—in particular the definition of a liability; and clarifications in important areas, such as the roles of stewardship, prudence and measurement uncertainty in financial reporting. These amendments are not expected to have any material impact on our consolidated financial statements. The following new standards and amendments to standards have been issued, but are not mandatory for the first time for the financial year beginning January 1, 2019 and have not been endorsed by the European Union. ■ Amendments to IFRS 9, IAS 39 and IFRS 7: Interest Rate Benchmark Reform (effective 1 January 2020). The amendments require qualitative and quantitative disclosures to enable users of financial statements to understand how an entity’s hedging relationships are affected by the uncertainty arising from interest rate benchmark reform. These amendments are not expected to have any material impact on our consolidated financial statements. ■ Amendments to the guidance of IFRS 3 Business Combinations, that revises the definition of a business (effective 1 January 2020). The new guidance provides a framework to evaluate when an input and a substantive process are present (including for early stage companies that have not generated outputs). To be a business without outputs, there will now need to be an organised workforce. The changes to the definition of a business will likely result in more acquisitions being accounted for as asset acquisitions across all industries, particularly real estate, pharmaceutical, and oil and gas. Application of the changes would also affect the accounting for disposal transactions. These amendments are not expected to have any material impact on our consolidated financial statements. ■ Amendments to the definition of material in IAS 1 and IAS 8 (effective 1 January 2020). The amendments clarify the definition of material and make IFRSs more consistent. The amendment clarifies that the reference to obscuring information addresses situations in which the effect is similar to omitting or misstating that information. It also states that an entity assesses materiality in the context of the financial statements as a whole. The amendment also clarifies the meaning of ‘primary users of general purpose financial statements’ to whom those financial statements are directed, by defining them as ‘existing and potential investors, lenders and other creditors’ that must rely on general purpose financial statements for much of the financial information they need. The amendments are not expected to have a significant impact on the preparation of financial statements. ■ Amendments to IAS 1 regarding the classification of liabilities as current or non-current (effective 1 January 2022). The amendments affect only the presentation of liabilities in the statement of financial position, not the amount or timing of recognition of any asset, liability, income or expense, or the information that entities disclose about those items. The amendments clarify that the classification of liabilities as current or non-current should be based on rights that are in existence at the end of the reporting period and align the wording in all affected paragraphs to refer to the "right" to defer settlement by at least twelve months and make explicit that only rights in place "at the end of the reporting period" should affect the classification of a liability. They also clarify that classification is unaffected by expectations about whether an entity will exercise its right to defer settlement of a liability and they make clear that settlement refers to the transfer to the counterparty of cash, equity instruments, other assets or services. The amendments are not expected to have a significant impact on the preparation of financial statements. These amendments are not expected to have any material impact on our consolidated financial statements. ■ IFRS 17 ‘Insurance contracts’ (effective 1 January 2022). This standard replaces IFRS 4, which currently permits a wide variety of practices in accounting for insurance contracts. IFRS 17 will fundamentally change the accounting by all entities that issue insurance contracts and investment contracts with discretionary participation features. This standard is not expected to have any material impact on our consolidated financial statements.
Segment reporting	2.23 Segment reporting Segment results include revenue and expenses directly attributable to a segment and the relevant portion of revenue and expenses that can be allocated on a reasonable basis to a segment. Segment assets and liabilities comprise those operating assets and liabilities that are directly attributable to the segment or can be allocated to the segment on a reasonable basis. Segment assets and liabilities do not include income tax items. The Company manages its activities and operates as one business unit which is reflected in its organizational structure and internal reporting. The Company does not distinguish in its internal reporting different segments, neither business nor geographical segments. The chief operating decision‑maker is the Board of Directors.

Significant accounting polici_3

Significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2019
Schedule of operating lease commitment to lease liabilities	(in thousands of €) Operating lease commitments disclosed as at December 31, 2018 € 3,004 Less: discounting effect using the lessee's incremental borrowing rate of the date of initial application € (126) Less: short-term leases recognized on a straight-line basis as expense € (88) Lease liability recognized as at January 1, 2019 € 2,790 of which are: Current lease liabilities € 1,078 Non-current lease liabilities € 1,712
IFRS 16
Schedule of cumulative effect of adoption	(in thousands of €) Property, plant and equipment (right-of-use assets) € 2,790 Effect on total assets € 2,790 Lease liabilities (current and non-current) € 2,790 Effect on total equity and liabilities € 2,790
IFRS 15
Schedule of cumulative effect of adoption	(in thousands of €) Balance at December 31, 2017 Adjustments due to adoption IFRS 15 Balance at January 1, 2018 Assets Prepaid expenses € 2,338 € (255) € 2,083 Liabilities Deferred revenue — non-current € 1,435 € 378 € 1,813 Deferred revenue — current 8,635 2,272 10,907 Equity Accumulated losses € (100,568) € (2,395) € (102,962)

Intangible assets (Tables)

Intangible assets (Tables)	12 Months Ended
	Dec. 31, 2019
Intangible assets
Schedule of intangible assets	(in thousands of €) Opening balance as on January 1, 2017 Intangibles acquired separately Software licenses Total Cost € — € 93 € 93 Accumulated amortization — (76) (76) Book value at the beginning of the year — 17 17 Movements Additions — 6 6 Amortization — (10) (10) Balance as on December 31, 2017 Cost — 99 99 Accumulated amortization — (86) (86) Book value at year end — 13 13 Movements Additions — 62 62 Cost of disposals — (2) (2) Amortization — (19) (19) Accumulated ammortization on disposals — 2 2 Balance as on December 31, 2018 Cost — 159 159 Accumulated amortization — (103) (103) Book value at year end — 56 56 Movements Additions 39,881 262 40,143 Amortization — (38) (38) Balance as on December 31, 2019 Cost 39,881 421 40,302 Accumulated amortization — (141) (141) Book value at year end € 39,881 € 280 € 40,161

Property, plant and equipment (

Property, plant and equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property, plant and equipment.
Schedule of property, plant and equipment	IT, office and lab Right-of-use assets Right-of-use assets Leasehold Lease (in thousands of €) equipment Buildings Vehicles improvements equipment (1) Total Opening balance as on January 1, 2017 Cost € 2,112 € — € — € — € — € 2,112 Accumulated depreciation (1,346) — — — — (1,346) Book value at the beginning of the year 766 — — — — 766 Movements Additions 346 — — — — 346 Cost of disposals (69) — — — — (69) Depreciation (425) — — — — (425) Accumulated depreciation on disposals 58 — — — — 58 Closing balance as on December 31, 2017 Cost 2,389 — — — — 2,389 Accumulated depreciation (1,713) — — — — (1,713) Book value at year end 676 — — — — 676 Movements Additions 370 — — — 253 623 Cost of disposals (47) — — — (46) Depreciation (463) — — — (11) (474) Accumulated depreciation on disposals 46 — — — 46 Closing balance as on December 31, 2018 Cost 2,712 — — — 253 2,965 Accumulated depreciation (2,130) — — — (11) (2,141) Book value at year end € 582 € — € — € — € 242 € 824 Adoption of IFRS 16 on January 1, 2019 € — € 2,338 € 452 — € — € 2,790 Movements Additions 765 4,553 525 808 29 6,680 Depreciation (460) (1,315) (233) (92) (28) (2,128) Closing balance as on December 31, 2019 Cost 3,477 6,891 977 808 282 12,435 Accumulated depreciation (2,590) (1,315) (233) (92) (39) (4,269) Book value at year end € 887 € 5,576 € 744 € 716 € 243 € 8,167

Research and development ince_2

Research and development incentive receivables (Tables)	12 Months Ended
	Dec. 31, 2019
Research and development incentive receivables
Schedule of research and development incentive receivables	Year Ended December 31, (in thousands of €) 2019 2018 2017 Research and development incentive receivables—current € 261 € 301 € 158 Research and development incentive receivables—non-current 8,566 4,883 3,033 € 8,827 € 5,184 € 3,191

Restricted cash (Tables)

Restricted cash (Tables)	12 Months Ended
	Dec. 31, 2019
Restricted cash
Schedule of restricted cash	Year Ended December 31, (in thousands of €) 2019 2018 2017 Non‑current restricted cash Rental guarantees € 630 € 251 € 256 Total non‑current € 630 € 251 € 256 Current restricted cash Escrow account < 1 year — 1,692 1,692 Total restricted cash € 630 € 1,943 € 1,948

Trade and other receivables (Ta

Trade and other receivables (Tables)	12 Months Ended
	Dec. 31, 2019
Trade and other receivables
Schedule of trade and other receivables	Year Ended December 31, (in thousands of €) 2019 2018 2017 VAT receivable € 1,121 € 496 € 317 Trade receivables 22,580 214 845 Other receivables 1,378 455 750 Interest receivable 2,081 556 — VLAIO grant receivable 955 1,165 930 € 28,115 € 2,886 € 2,842

Cash and cash equivalents (Tabl

Cash and cash equivalents (Tables)	12 Months Ended
	Dec. 31, 2019
Cash and cash equivalents
Schedule of cash and cash equivalents	Year Ended December 31, (in thousands of €) 2019 2018 2017 Cash equivalents € 252,550 € 217,626 € 25,000 Cash and bank balances 78,732 63,414 165,867 € 331,282 € 281,040 € 190,867

Share capital and share premi_2

Share capital and share premium (Tables)	12 Months Ended
	Dec. 31, 2019
Share capital and share premium
Schedule of number of shares outstanding	Number of shares outstanding on January 1, 2017 20,126,479 U.S. initial public offering on Nasdaq on May 17, 2017 5,865,000 Over-allotment option exercised by underwriters on May 19, 2017 879,750 Exercise of options in August 2017 5,000 Exercise of options in September 2017 15,000 Exercise of options in October 2017 1,400 Exercise of options in November 2017 106,782 U.S. second public offering on Nasdaq on December 13, 2017 4,440,000 Over-allotment option exercised by underwriters on December 14, 2017 666,000 Exercise of options in December 2017 75,230 Number of shares outstanding on December 31, 2017 32,180,641 Exercise of options in January 2018 111,727 Exercise of options in March 2018 113,075 Exercise of options in April 2018 34,039 Exercise of options in May 2018 5,900 Exercise of options in June 2018 5,393 Exercise of options in July 2018 469 Exercise of options in August 2018 2,300 Exercise of options in September 2018 5,913 U.S. third public offering on Nasdaq on September 18, 2018 3,475,000 Exercise of options in October 2018 556 Exercise of options in November 2018 9,768 Exercise of options in December 2018 30,531 Number of shares outstanding on December 31,2018 35,975,312 Exercise of options in January 2019 163,170 Share subscription from Johnson & Johnson Innovation Inc. 1,766,899 Exercise of options in February 2019 13,393 Exercise of options in March 2019 73,005 Exercise of options in April 2019 13,729 Exercise of options in May 2019 35,054 Exercise of options in June 2019 66,965 Exercise of options in July 2019 56 Exercise of options in August 2019 8,710 Exercise of options in September 2019 5,730 Exercise of options in October 2019 611 Global public offering on Euronext and Nasdaq on November 7, 2019 4,000,000 Over-allotment option exercised by underwriters on November 8, 2019 600,000 Exercise of options in November 2019 16,714 Exercise of options in December 2019 22,180 Number of shares outstanding on December 31,2019 42,761,528

Share-based payments (Tables)

Share-based payments (Tables)	12 Months Ended
	Dec. 31, 2019
Share-based payments
Schedule of share based payment arrangement	Exercise price Outstanding per stock stock options on options December 31, Expiry date (in €) 2019 2018 2017 2020 € 3.95 7,210 18,200 36,960 2021 3.95 — — 2,850 2023 2.44 211,769 294,400 314,593 2024 2.44 96,696 117,733 135,890 2024 3.95 6,238 6,895 15,692 2024 7.17 335,067 407,061 516,100 2024 2.44 6,000 26,970 83,820 2025 11.44 39,000 39,000 39,000 2025 10.34 3,000 3,000 3,000 2025 9.47 185,832 226,323 235,514 2026 11.38 45,000 50,415 60,000 2026 11.47 219,791 257,616 282,310 2026 14.13 258,746 315,102 362,126 2027 18.41 108,613 114,019 120,536 2027 21.17 565,798 628,292 653,825 2023 80.82 94,100 94,600 — 2028 80.82 73,100 75,450 — 2023 86.32 366,260 369,760 — 2028 86.32 402,714 491,815 — 2024 113.49 111,690 — — 2029 113.49 279,760 — — 2029 113.49 19,800 2024/2029 (1) € 135.75 921,885 — — 4,358,069 3,536,651 2,862,216 (1) On December 20, 2019, the Company granted options for which the beneficiaries had a 60-day period to choose between a contractual term of five or ten years.
Schedule of number of stock options	2019 2018 2017 Number of Weighted average Number of Weighted average Number of Weighted average stock options exercise price stock options exercise price stock options exercise price Outstanding at January 1 3,536,651 € 33.42 2,862,216 € 11.54 2,293,636 € 7.72 Granted 1,365,172 128.52 1,040,475 85.37 774,361 20.74 Exercised (419,317) 11.35 (319,671) 7.02 (203,412) 3.46 Forfeited (124,437) 88.92 (46,369) 30.44 (2,369) 12.52 Outstanding at December 31, 4,358,069 63.75 3,536,651 33.42 2,862,216 11.54 Exercisable at December 31, 2,203,476 € 22.59 1,859,315 € 9.62 1,598,829 € 6.80
Schedule of weighted average remaining contractual life for each range of exercise price:	Weighted average remaining Outstanding on contractual life Exercise price (in €) December 31, 2019 (in years) 2.44-3.95 327,913 3.95 7.17-9.47 520,899 5.32 10.34-14.13 565,537 6.59 18.41-21.17 674,411 7.88 80.82-86.32 936,174 6.43 113.49-135.75 1,333,135 9.41
Schedule of parameters used in relation to the new grants	Below is an overview of the parameters used in relation to the determination of the fair value of the grants during 2019: Stock options granted in June 2019 Nov 2019 Dec 2019 Number of options granted 423,487 19,800 921,885 Average fair value of options (in EUR) € 63.45 € 57.69 € 65.72 Share price (in EUR) € 123.20 € 126.40 € 146.40 Exercise price (in EUR) € 113.49 € 113.49 € 135.75 Expected volatility 45.25 % 44.14 % 44.18 % Average expected option life (in years) 8.59 6.50 6.50 (1) Risk‑free interest rate 0.07 % (0.05) % 0.03 % Expected dividends — % — % — % (1) On December 20, 2019, the Company granted a total of 921,885 stock options. The beneficiary can choose between a contractual term of five or ten years. The average expected option life is currently estimated at six and a half years. This estimate will be reassessed once the acceptance period of 60 days has passed and the beneficiaries will have made a choice between a contractual term of five or ten years. The total fair value of the grant would range from €49.5 million (100% of the stock options at an expected option life of four years) to €60.6 million (100% of the stock options at an expected option life of six and a half years). Below is an overview of the parameters used in relation to the determination of the fair value of grants during 2018: Stock options granted in June 2018 Dec 2018 Number of options granted 178,900 861,575 Average fair value of options (in EUR) € 32.12 € 39.85 Share price (in EUR) € 72.00 € 82.20 Exercise price (in EUR) € 80.82 € 86.32 Expected volatility 45.50 % 46.19 % Average expected option life (in years) 7.36 7.83 Risk‑free interest rate 0.72 % 0.77 % Expected dividends — % — % Below in an overview of the parameter used in relation to the determination of the fair value of grants during 2017: Stock options granted in June 2017 Dec 2017 Number of options granted 120,536 653,825 Average fair value of options (in EUR) € 7.90 € 37.10 Share price (in EUR) € 17.76 € 53.50 Exercise price (in EUR) € 18.41 € 21.17 Expected volatility 36.6 % 36.1 % Average expected option life (in years) 10 10 Risk‑free interest rate 0.61 % 0.53 % Expected dividends — % — %

Provision for employee benefi_2

Provision for employee benefits (Tables)	12 Months Ended
	Dec. 31, 2019
Provision for employee benefits
Schedule of amounts recognized	(in thousands of €) 2019 2018 2017 Defined benefit obligation € 1,789 € 1,277 € 1,007 Fair value of plan assets 1,725 1,270 982 Deficit / surplus (−) of funded obligations 64 7 25 Net liability (asset) € 64 € 7 € 25
Schedule of movement in the defined benefit obligation, plan assets, net liability and asset	(in thousands of €) 2019 2018 2017 Defined benefit obligation at January 1 € 1,277 € 1,007 € 670 Service cost 379 336 352 Interest expense 19 15 11 Contributions by plan participants (167) (116) (148) Actuarial gains (-) / losses (+) 281 35 124 Benefits paid / transfers out — — (2) Defined benefit obligation at December 31 € 1,789 € 1,277 € 1,007 (in thousands of €) 2019 2018 2017 Fair value of plan assets at January 1 € 1,270 € 982 € 669 Interest income 19 16 10 Administrative costs & taxes (47) (32) (46) Contributions by company & participants 475 328 423 Contributions by plan participants (168) (116) (148) Actuarial gains (+) / losses (-) 176 92 76 Benefits paid / transfers out — — (2) Fair value of plan assets at December 31 € 1,725 € 1,270 € 982
Schedule of actuarial assumption	Actuarial assumption 2019 2018 2017 Discount rate 1.0 % 1.3 % 1.3 %
Schedule of sensitivity analyses	Sensitivity analysis Change in Impact on defined ‑ (in thousands of €) assumption benefit obligation % Discount rate -0.25 % Increase by 45.5 2.54 % Discount rate 0.25 % Decrease by (33.7) 1.88 %

Trade and other payables (Table

Trade and other payables (Tables)	12 Months Ended
	Dec. 31, 2019
Trade and other payables
Schedule of trade and other payables	Year Ended December 31, (in thousands of €) 2019 2018 2017 Trade payables € 9,360 € 6,007 € 4,395 Accruals for invoices to be received 49,069 18,145 4,046 Short‑term employee benefits 26,872 12,920 6,844 € 85,301 € 37,072 € 15,285

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2019
Revenue
Schedule of revenue	Year Ended December 31, (in thousands of €) 2019 2018 2017 Upfront payments € 22,360 € 8,635 € 20,137 Milestone payments 28,085 11,440 9,677 Research and development service fees 19,338 1,407 6,601 € 69,783 € 21,482 € 36,415

Other operating income (Tables)

Other operating income (Tables)	12 Months Ended
	Dec. 31, 2019
Other operating income
Schedule of other operating income	Year Ended December 31, (in thousands of €) 2019 2018 2017 Grants € 2,289 € 1,842 € 422 Research and development incentives 4,818 2,151 983 Payroll tax rebates 5,694 3,756 3,436 € 12,801 € 7,749 € 4,841
Schedule of grants	(Amounts presented in thousands of €) Flanders Innovation & Entrepreneurship - VLAIO 1 Grantor: Flanders Innovation & Entrepreneurship Agency Start date: 01/11/2017 End date: 31/10/2020 Amount granted and approved: € 2,527 Amount recognized: 845 Flanders Innovation & Entrepreneurship - VLAIO 2 Grantor: Flanders Innovation & Entrepreneurship Agency Start date: 01/05/2018 End date: 31/10/2020 Amount granted and approved: € 2,634 Amount recognized: 1,411

Segment reporting (Tables)

Segment reporting (Tables)	12 Months Ended
	Dec. 31, 2019
Segment reporting
Schedule of external customers geographically location	Revenue from external customers Year ended December 31, (in thousands of €) 2019 2018 2017 Netherlands € € 470 € 628 Belgium 1,498 — — Denmark 436 1,136 6,240 Switzerland 40,593 912 2,486 United States — — 1 Luxembourg 27,256 18,964 27,060 Total € 69,783 € 21,482 € 36,415 Non-current assets Year ended December 31, (in thousands of €) 2019 2018 2017 Netherlands € 1 € 1 € 1 Belgium 56,777 5,967 4,103 United States 3,058 47 — Japan 284 — — Total € 60,120 € 6,015 € 4,104

Research and development expe_2

Research and development expenses (Tables)	12 Months Ended
	Dec. 31, 2019
Research and development expenses
Schedule of research and development expenses	Year Ended December 31, (in thousands of €) 2019 2018 2017 Personnel expense € 45,733 € 26,519 € 16,473 External research and development expenses 137,050 48,859 27,893 Materials and consumables 2,027 1,464 1,562 Depreciation and amortization 1,641 494 446 Other expenses 11,214 6,273 5,366 € 197,665 € 83,609 € 51,740

Selling, general and administ_2

Selling, general and administrative expenses (Tables)	12 Months Ended
	Dec. 31, 2019
Selling, general and administrative expenses
Schedule of selling, general and administrative expenses	Year Ended December 31, (in thousands of €) 2019 2018 2017 Personnel expense € 40,082 € 18,292 € 6,745 Consulting fees 5,624 3,646 3,289 Marketing costs 10,719 1,826 — Supervisory board 2,792 1,088 621 Office costs 5,352 2,619 1,793 € 64,569 € 27,471 € 12,448

Personnel expenses (Tables)

Personnel expenses (Tables)	12 Months Ended
	Dec. 31, 2019
Personnel expenses
Schedule of personnel expenses	Year Ended December 31, (in thousands of €) 2019 2018 2017 Short ‑ term employee benefits—Salaries € 32,866 € 18,617 € 12,149 Short ‑ term employee benefits—Social Security 3,555 2,213 1,504 Post ‑ employment benefits 748 441 291 Termination benefits 644 96 8 Share ‑ based payment 37,208 18,527 3,985 Employer social security contributions stock options 10,794 4,918 5,281 € 85,815 € 44,812 € 23,218
Schedule of full-time equivalents employees	Year Ended December 31, Number of FTE 2019 2018 2017 Research and development 116.9 74.4 56.8 Selling, general and administrative 69.2 29.5 14.7 186.1 103.9 71.5

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases
Schedule of financial position relating to leases	As on As on December 31, January 1, In thousands of € 2019 2019 Right-of-use assets Buildings € 5,576 € 2,338 Vehicles 744 525 Equipment 243 242 € 6,564 € 3,105 Lease liabilities Current € 1,974 € 1,078 Non-current 4,540 1,712 € 6,514 € 2,790
Schedule of maturity analysis of the lease liabilities	(in thousands of €) Less than 1 year 1-3 years 3-5 years More than 5 years Total contractual cash flows Carrying amount Lease liabilities € 2,205 € 3,137 € 1,251 € 432 € 7,025 € 6,514
Schedule of total lease liabilities recognized in our statement of financial position	Year Ended December 31, In thousands of € 2019 2018 2017 Depreciation charges Buildings € 1,315 € — € — Vehicles 233 — — Equipment 28 11 — € 1,576 € 11 € — Interest expense (included in finance cost) € 105 € — € — Expense relating to short-term leases 123 — — Expense relating to leases of low-value assets that are not shown above as short-term leases 5 — —

Financial result and exchange_2

Financial result and exchange gains/(losses) (Tables)	12 Months Ended
	Dec. 31, 2019
Financial result and exchange gains/(losses)
Schedule of financial result and exchange gains/(losses)	Year Ended December 31, (in thousands of €) 2019 2018 2017 Interest income on bank deposits € 7,874 € 1,371 € 165 Net gains on current financial assets at FVTPL 6,525 2,323 210 Realized gain on non-current financial assets — — 875 Financial income 14,399 3,694 1,250 Financial expense (124) — — Realized exchange gains/(losses) (338) 1,355 — Unrealized exchange gains/(losses) 6,404 10,953 (5,797) Exchange gains/(losses) 6,066 12,308 (5,797)

Income tax expense (Tables)

Income tax expense (Tables)	12 Months Ended
	Dec. 31, 2019
Income tax expense
Schedule of income tax expenses	Year Ended December 31, (in thousands of €) 2019 2018 2017 Loss before taxes (158,213) (65,847) (27,479) Income tax calculated at 25% 39,553 16,462 6,870 Effect of expenses that are not deductible in determining taxable results (7,701) (3,934) (1,141) Effect of stock issue expenses that are not deductible in determining taxable results 5,750 3,716 5,754 Effect of concessions (R&D incentives and grants) 572 430 453 Effect of tax losses carried forward not recognized (Netherlands) (356) — — Effect of usage of tax losses carried forward not previously recognized (Netherlands) — — 19,378 Effect of tax losses carried forward not recognized (Belgium) (11,314) (5,511) (27,413) Effect of adjustments for current tax of prior periods (Belgium) (3,876) — — Effect of change in corporate tax rate on deferred tax asset not previously recognized (Belgium) — — 373 Effect of different tax rates in jurisdictions in which the company operates (52) (15) (517) Deferred tax asset other than loss carryforwards not recognized (27,341) (11,968) (4,363) Other 13 26 9 Income tax expense recognized in the consolidated statement of profit and loss € (4,752) € (794) € (597)

Loss per share (Tables)

Loss per share (Tables)	12 Months Ended
	Dec. 31, 2019
Loss per share
Schedule of loss per share	Year Ended December 31, (in thousands of €) 2019 2018 2017 Loss of the year € (162,965) € (66,641) € (28,076) Weighted average number of shares outstanding 38,619,121 33,419,356 24,609,536 Basic and diluted loss per share (in €) € (4.22) € (1.99) € (1.14)

Financial instruments and fin_2

Financial instruments and financial risk management (Tables)	12 Months Ended
	Dec. 31, 2019
Financial instruments and financial risk management
Schedule of overview of financial instruments	Measurement category Carrying amount Year Ended December 31, (in thousands of €) 2019 2018 2017 (1) Financial assets — non-current FVTPL € 2,596 1 € 1 Research and development incentive receivables — non-current Amortised cost 8,566 4,883 3,033 Restricted cash — non-current Amortised cost 630 251 256 Trade and other receivables Amortised cost 28,115 2,886 2,842 Prepaid expenses Amortised cost 9,022 2,995 2,338 Financial assets—current FVTPL 1,004,539 283,529 168,907 Research and development incentive receivables — current Amortised cost 261 301 158 Restricted cash — current Amortised cost — 1,692 1,692 Cash and cash equivalents Amortised cost 331,282 281,040 190,867 Trade and other payables Amortised cost 85,301 37,072 15,285 (1) The Company adopted IFRS 9 on January 1, 2018. Under IAS 39, non-current financial assets were measured as “Available for sale”.
Schedule of assets at fair value	At December 31,2019 (in thousands of €) Level 1 Level 2 Level 3 Non-current financial assets € € € 2,596 Current financial assets 1,004,539 Assets carried at fair value € 1,004,539 € — € 2,596 At December 31,2018 (in thousands of €) Level 1 Level 2 Level 3 Non-current financial assets € € € 1 Current financial assets 283,529 Assets carried at fair value € 283,529 € — € 1 At December 31,2017 (in thousands of €) Level 1 Level 2 Level 3 Non-current financial assets € € € 1 Current financial assets 168,907 Assets carried at fair value € 168,907 € — € 1
Schedule of net exposure exchange differences of the monetary assets	At December 31, (in thousands of €) 2019 2018 2017 USD 821,916 312,831 147,169 JPY 488 — — GBP 4 2 406 CHF 1 4 25

Related party transactions (Tab

Related party transactions (Tables)	12 Months Ended
	Dec. 31, 2019
Disclosure of transactions between related parties [line items]
Schedule of remuneration of key management personnel	Year Ended December 31, (in thousands of €) 2019 2018 2017 Short term employee benefits € 4,437 € 4,236 € 3,126 Post employment benefits 144 153 115 Termination benefits 470 — — Share ‑ based payment (1) 21,847 13,363 12,041 Employer social security contributions stock options (2) 9,160 2,792 3,073 € 36,058 € 20,544 € 18,355 (1) Amount shown represents the expenses with respect to the option awards granted in the year, measured using the Black Scholes formula. The share-based payment expense recognized in the consolidated statement of comprehensive income totaled €14.4 million for the year ended December 31, 2019, compared to €10.7 million for the year ended December 31, 2018 and €2.3 million for the year ended December 31, 2017 (2) The Company incurs employer social security costs with respect to the option awards granted to certain members of the executive management. The amount of employer social security costs depends on the actual economic value realized and therefore varies based on our stock price. At each reporting date, the Company makes a calculation of the exposure.
Schedule of number of stock options	2019 2018 2017 Number of Weighted average Number of Weighted average Number of Weighted average stock options exercise price stock options exercise price stock options exercise price Outstanding at January 1 3,536,651 € 33.42 2,862,216 € 11.54 2,293,636 € 7.72 Granted 1,365,172 128.52 1,040,475 85.37 774,361 20.74 Exercised (419,317) 11.35 (319,671) 7.02 (203,412) 3.46 Forfeited (124,437) 88.92 (46,369) 30.44 (2,369) 12.52 Outstanding at December 31, 4,358,069 63.75 3,536,651 33.42 2,862,216 11.54 Exercisable at December 31, 2,203,476 € 22.59 1,859,315 € 9.62 1,598,829 € 6.80
Executive Directors
Disclosure of transactions between related parties [line items]
Schedule of remuneration of key management personnel	Pension 2017 Base salary Bonus contributions Social security costs ESOP (1) Other (2) Total Tim Van Hauwermeiren 303,941 301,635 14,315 9,459 2,968,195 9,601 3,607,146 Eric Castaldi 271,344 173,284 62,335 254,732 4,089,209 14,979 4,865,883 Total 575,285 474,919 76,650 264,191 7,057,404 24,580 8,473,029 Pension 2018 Base salary Bonus contributions Social security costs ESOP (1) Other (2) Total Tim Van Hauwermeiren 500,000 284,600 15,102 10,011 3,559,200 33,855 4,402,768 Total 500,000 284,600 15,102 10,011 3,559,200 33,855 4,402,768 Pension 2019 Base salary Bonus contributions Social security costs ESOP (1) Other (2) Total Tim Van Hauwermeiren 525,000 326,288 21,532 10,587 5,257,360 11,558 6,152,325 Total 525,000 326,288 21,532 10,587 5,257,360 11,558 6,152,325 (1) Amount shown represents the expenses with respect to the option awards granted in the year, measured using the Black Scholes formula, and the employer social security costs with respect to the option awards granted to certain members of the executive management. The amount of employer social security costs depends on the actual economic value realized and therefore varies based on our stock price. At each reporting date, the Company makes a calculation of the exposure. (2) Consists of rent paid by the Company, costs attributable to the lease of a company car and employer-paid medical insurance premiums.
Schedule of weighted average contractual term	Name Number of options Remaining term at December 31, 2019 (rounded up) Tim Van Hauwermeiren 35,000 5.0 years 30,600 6.0 years 50,000 6.5 years 30,600 7.0 years 80,000 8.0 years 80,000 9.0 years 80,000 10.0 years
Schedule of number of stock options	The table below shows the number of stock options granted to the executive directors during the years ended December 31, 2019, 2018 and 2017 and their exercise price equal to the fair market value upon date of grant, and the stock options exercised during 2019, 2018 and 2017. 2017 ESOPs Term Exercise price Exercised Tim Van Hauwermeiren 80,000 10 years 21.17 2.44 65,380 Eric Castaldi 43,200 years 21.17 Total 123,200 65,380 2018 ESOPs Term Exercise price Exercised Tim Van Hauwermeiren 80,000 10 years 86.32 7.17 40,000 Total 80,000 40,000 2019 ESOPs Term Exercise price Exercised Tim Van Hauwermeiren 80,000 10 years 135.75 7.17 30,000 Total 80,000 30,000 The table below shows the stock options held at the start of the year ended December 31, 2019, the stock options granted to executive directors which have vested during the year ended December 31, 2019 and the stock options to vest in the years until 2022. Total Total options options Options held on options options held on vested Options Options Options Options January 1, granted in exercised in December 31, until Exercise vested in Exercise to vest Exercise to vest Exercise to vest Exercise Name 2019 2019 2019 2019 2018 price 2019 price 2020 price 2021 price 2022 price Tim Van Hauwermeiren 336,200 80,000 (30,000) 386,200 35,000 7.17 30,600 9.47 43,056 6,944 20,400 10,200 26,667 26,666 21.17 26,667 21.17 21.17 26,667 86.32 26,666 86.32 26,667 86.32 26,667 135.75 26,666 135.75 26,667 135.75
Non-executive Directors
Disclosure of transactions between related parties [line items]
Schedule of remuneration of key management personnel	2019 2018 2017 Peter Verhaeghe € 77,500 € 77,500 € 77,500 David L Lacey 50,000 50,000 50,000 Werner Lanthaler 55,000 55,000 55,000 Pamela Klein 42,500 42,500 42,500 Don Debethizy 52,500 52,500 52,500 A.A. Rosenberg 50,000 42,500 42,500 James M. Daly 50,000 35,000 — Total € 377,500 € 355,000 € 320,000
Schedule of weighted average contractual term	Remaining term on Number of December 31, 2019 Name stock options (rounded up) Peter K.M. Verhaeghe 3,650 0.5 years 2,340 1.0 years 5,560 3.5 years 3,181 4.0 years 9,854 5.0 years 10,000 6.5 years 10,000 9.0 years 10,000 10.0 years David L. Lacey 3,180 3.5 years 1,818 4.0 years 14,445 5.0 years 10,000 6.5 years 15,000 8.0 years 10,000 9.0 years 10,000 10.0 years Werner Lanthaler 10,000 9.0 years 10,000 10.0 years J. Donald deBethizy 15,000 5.5 years 10,000 6.5 years 10,000 9.0 years 10,000 10.0 years Pamela Klein 15,000 5.5 years 10,000 6.5 years 10,000 9.0 years 10,000 10.0 years A.A. Rosenberg 15,000 7.0 years 10,000 9.0 years 10,000 10.0 years James M. Daly 15,000 8.5 years 10,000 9.0 years 10,000 10.0 years
Schedule of number of stock options	The table below shows the number of stock options granted to the non-executive directors during the years ended December 31, 2019, 2018 and 2017 and their exercise price, based on the 30 day average stock price prior to their date of grant, and the stock options exercised during the years ended December 31, 2019, 2018 and 2017. 2017 ESOPs Term Exercise price Exercised David L Lacey 15,000 10 years 21.37 Total 15,000 — 2018 ESOPs Term Exercise price Exercised James M. Daly 15,000 10 years 80.82 Peter Verhaeghe 10,000 10 years 86.32 David L Lacey 10,000 10 years 86.32 Werner Lanthaler 10,000 10 years 86.32 2.44 3,566 7.17 5,000 2.44 10,850 11.38 5,556 Don Debethizy 10,000 10 years 86.32 Pamela Klein 10,000 10 years 86.32 A.A. Rosenberg 10,000 10 years 86.32 James M. Daly 10,000 10 years 86.32 Total 85,000 24,972 2019 ESOPs Term Exercise price Exercised Peter Verhaeghe 10,000 10 years 135.75 David L Lacey 10,000 10 years 135.75 Werner Lanthaler 10,000 10 years 135.75 11.38 4,444 Pamela Klein 10,000 10 years 135.75 Don Debethizy 10,000 10 years 135.75 A.A. Rosenberg 10,000 10 years 135.75 James M. Daly 10,000 10 years 135.75 Total 70,000 4,444 The table below shows the stock options held at the start of the year ended December 31, 2019 and the stock options granted to the non‑executive directors which have vested during the year ended December 31, 2019, as well as the stock options to vest in the years ending December 31, 2020, December 31, 2021 and December 31, 2022 (in number of stock options), and the respective exercise price of such stock options: Total Total Options Options Options options Options Options options Options Options to to to held on granted exercised held on vested vested vest vest vest January 1, in in December 31, until Exercise in Exercise in Exercise in Exercise in Exercise Name 2019 2019 2019 2019 2018 price 2019 price 2020 price 2021 price 2022 price Peter Verhaeghe 44,585 10,000 54,585 11,626 € 2.44 7,959 € 3.95 5,000 € 7.17 8,333 € 11.38 1,667 € 11.38 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 David L. Lacey 54,443 10,000 64,443 6,643 € 2.44 12,800 € 7.17 8,333 € 11.38 1,667 € 11.38 5,000 € 21.17 5,000 € 21.17 5,000 € 21.17 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 Werner Lanthaler 14,444 10,000 (4,444) 20,000 — € 2.44 — € 7.17 — € 11.38 — € 11.38 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 J. Donald deBethizy 35,000 10,000 45,000 15,000 € 11.44 8,333 € 11.38 1,667 € 11.38 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 Pamela Klein 35,000 10,000 45,000 15,000 € 11.44 8,333 € 11.38 1,667 € 11.38 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 A.A. Rosenberg 25,000 10,000 35,000 10,000 € 14.13 5,000 € 14.13 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75 James M. Daly 25,000 10,000 35,000 7,500 € 80.82 5,000 € 80.82 2,500 € 80.82 3,333 € 86.32 3,334 € 86.32 3,333 € 86.32 3,333 € 135.75 3,334 € 135.75 3,333 € 135.75

Audit fees (Tables)

Audit fees (Tables)	12 Months Ended
	Dec. 31, 2019
Audit fees
Schedule of auditors' fees expensed in the income statement	Year Ended December 31, Fees 2019 2018 2017 in thousands of € Audit fees (1) € 730 € 648 € 179 Audit-related fees 159 143 724 Tax and other services (2) — — — Total € 889 € 791 € 903 (1) Audit services performed by Deloitte Accountants B.V. as the external auditor referred to in Section 1 of the Dutch Accounting Firms Oversight Act (Wta) as well as by the Deloitte network. (2) Tax and other services performed by the Deloitte network.

Overview of consolidation sco_2

Overview of consolidation scope (Tables)	12 Months Ended
	Dec. 31, 2019
Overview of consolidation scope
Schedule of overview of subsidiaries	Name Registration number Country Participation Main activity argenx SE COC 24435214 The Netherlands 100.00 % Holding company argenx BV Belgium 100.00 % Biotechnical research on drugs and pharma processes argenx US, Inc. 36-4880497 USA 100.00 % Pharmaceuticals and pharmacy supplies merchant wholesalers argenx Japan KK 0104-01-145183 Japan 100.00 % Pharmaceuticals and pharmacy supplies merchant wholesalers

Significant accounting polici_4

Significant accounting policies - Property, plant and equipment and Others (Details) € in Thousands	12 Months Ended
	Dec. 31, 2019EUR (€)item	Dec. 31, 2018EUR (€)
Property, plant and equipment
Impairment of assets	€ 0
Minimum Refund Period of Research and Development Incentives	5 years	5 years
Profit available for distribution		€ 0
Number of operating segments | item	1
IT equipment
Property, plant and equipment
Estimated useful life	3 years
Minimum | Office and lab equipment
Property, plant and equipment
Estimated useful life	3 years
Maximum | Office and lab equipment
Property, plant and equipment
Estimated useful life	5 years

Significant accounting polici_5

Significant accounting policies - Retirement Benefits (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Significant accounting policies
Historical minimum guaranteed rates of return on employer contributions	3.25%
Historical minimum guaranteed rates of return on employee contributions	3.75%
Minimum return rate on defined contribution pension plans	1.75%	1.75%
Maximum return rate on defined contribution pension plans	3.75%	3.75%

Significant accounting polici_6

Significant accounting policies - Cumulative effect of adopting IFRS15 (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
Assets
Prepaid expenses	€ 9,022	€ 2,995	€ 2,995	€ 2,338	€ 2,083
Liabilities
Deferred revenue — non-current	218,032			1,435	1,813
Deferred revenue - current	72,338	2,161	2,161	8,635	10,907
Equity
Accumulated losses	(332,568)	(169,603)	(169,603)	(100,568)	(102,962)
Consolidated statement of profit and loss and other comprehensive income
Revenue	69,783		21,482	36,415
Research and development expenses	(197,665)		(83,609)	(51,740)
Loss for the year and total comprehensive loss	(162,965)	€ (66,641)	(66,641)	(28,076)
Consolidated statement of cash flows
Operating result	(178,554)		(81,849)	(22,932)
Movements in Current Assets or Liabilities [Abstract]
(Increase)/decrease in other current assets	(5,170)		(800)	(1,093)
Increase/(decrease) in deferred revenue — current	62,106		(8,868)	(11,501)
Cash flows (used in)/from operating activities	€ 139,064		€ (53,274)	€ (36,546)
Adjustments due to adoption IFRS 15
Assets
Prepaid expenses					255
Liabilities
Deferred revenue — non-current					378
Deferred revenue - current					2,272
Equity
Accumulated losses					€ (2,395)

Significant accounting polici_7

Significant accounting policies - New accounting policies and disclosures (Details) - EUR (€) € in Thousands	Jan. 01, 2019	Dec. 31, 2019	Dec. 31, 2018
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Operating lease commitments			€ 3,004
Less: discounting effect using the lessee's incremental borrowing rate of the date of initial application	€ (126)
Less: short-term leases recognized on a straight-line basis as expense	(88)	€ (123)
Lease liabilities	2,790	6,514
Current lease liabilities	1,078	1,974
Non-current lease liabilities	€ 1,712	€ 4,540
IFRS 16
Disclosure of expected impact of initial application of new standards or interpretations [line items]
Weighted average lessee's incremental borrowing rate applied to lease liabilities recognised at date of initial application of IFRS 16	1.32%

Significant accounting polici_8

Significant accounting policies - Cumulative effect of adopting IFRS 16 (Details) - EUR (€) € in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of initial application of standards or interpretations [line items]
Property, plant and equipment (right-of-use assets)	€ 6,564	€ 3,105
Lease liabilities (current and non-current)	6,514	2,790
Effect on total equity and liabilities	€ 1,433,339		€ 578,458	€ 370,908
Increase (decrease) due to application of IFRS 16
Disclosure of initial application of standards or interpretations [line items]
Property, plant and equipment (right-of-use assets)		2,790
Effect on total assets		2,790
Lease liabilities (current and non-current)		2,790
Effect on total equity and liabilities		€ 2,790

Critical accounting judgement_2

Critical accounting judgements and key sources of estimation uncertainty - (Details) € in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019EUR (€)	Dec. 31, 2019USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2018EUR (€)	Dec. 31, 2017EUR (€)	Dec. 31, 2019USD ($)
Notes to unaudited condensed consolidated interim statement of profit and loss and other comprehensive income
Revenue.	€ 69,783			€ 21,482	€ 36,415
Upfront Payments Received	22,360			8,635	20,137
Equity investment	678,936		€ 255,721		327,700
Research and development cost accruals	49,069		18,145	18,145	€ 4,046
Collaboration and license agreement
Notes to unaudited condensed consolidated interim statement of profit and loss and other comprehensive income
Revenue.	21,600
Deferred revenue			€ 1,200	€ 1,200
Cilag GmbH International | Collaboration and license agreement
Notes to unaudited condensed consolidated interim statement of profit and loss and other comprehensive income
Deferred revenue	289,000
Upfront Payments Received | $		$ 500
License payment committed | $						$ 300
Equity investment | $		$ 200
Clinical Manufacturing Organizations
Notes to unaudited condensed consolidated interim statement of profit and loss and other comprehensive income
Research and development cost accruals	€ 44,000

Intangible assets (Details)

Intangible assets (Details) € in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019EUR (€)	Dec. 31, 2019USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2017EUR (€)
Intangible assets
Intangible assets other than goodwill at beginning of period	€ 56		€ 13	€ 17
Additions	40,143		62	6
Cost of disposals			(2)
Amortization	(38)		(19)	(10)
Intangible assets other than goodwill at end of period	40,161		56	13
Upfront payment | $		$ 30
Development milestone payment | $		$ 10
Commitments to acquire additional intangible assets	0
Intangible assets are pledged as security	0
Software
Intangible assets
Intangible assets other than goodwill at beginning of period	56		13	17
Additions	262		62	6
Cost of disposals			(2)
Amortization	(38)		(19)	(10)
Intangible assets other than goodwill at end of period	€ 280		56	13
Amortization period	3 years	3 years
Intangibles acquired separately
Intangible assets
Additions	€ 39,881
Intangible assets other than goodwill at end of period	39,881
Intangibles not yet available for use
Intangible assets
Development milestone payment | $		$ 5
Cost
Intangible assets
Intangible assets other than goodwill at beginning of period	159		99	93
Intangible assets other than goodwill at end of period	40,302		159	99
Cost | Software
Intangible assets
Intangible assets other than goodwill at beginning of period	159		99	93
Intangible assets other than goodwill at end of period	421		159	99
Cost | Intangibles acquired separately
Intangible assets
Intangible assets other than goodwill at end of period	39,881
Accumulated depreciation and amortization
Intangible assets
Intangible assets other than goodwill at beginning of period	(103)		(86)	(76)
Cost of disposals				2
Intangible assets other than goodwill at end of period	(141)		(103)	(86)
Accumulated depreciation and amortization | Software
Intangible assets
Intangible assets other than goodwill at beginning of period	(103)		(86)	(76)
Cost of disposals				2
Intangible assets other than goodwill at end of period	€ (141)		€ (103)	€ (86)

Property, plant and equipment_2

Property, plant and equipment (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, plant and equipment
Property, plant and equipment at beginning of period	€ 2,790	€ 676	€ 766
Additions	6,680	623	346
Depreciation	(2,128)	(474)	(425)
Property, plant and equipment at end of period	8,167	824	676
Commitments to acquire property, plant and equipment	0
Assets are pledged as security for liabilities	0
Office and lab equipment
Property, plant and equipment
Property, plant and equipment at beginning of period		676	766
Additions	765	370	346
Depreciation	(460)	(463)	(425)
Property, plant and equipment at end of period	887	582	676
Buildings
Property, plant and equipment
Property, plant and equipment at beginning of period	2,338
Additions	4,553
Depreciation	(1,315)
Property, plant and equipment at end of period	5,576
Vehicles
Property, plant and equipment
Property, plant and equipment at beginning of period	452
Additions	525
Depreciation	(233)
Property, plant and equipment at end of period	744
Leasehold improvements
Property, plant and equipment
Additions	808
Depreciation	(92)
Property, plant and equipment at end of period	716
Lease equipment
Property, plant and equipment
Additions	29	253
Depreciation	(28)	(11)
Property, plant and equipment at end of period	243	242
Cost
Property, plant and equipment
Property, plant and equipment at beginning of period		2,389	2,112
Sales and disposals		(46)	(69)
Property, plant and equipment at end of period	12,435	2,965	2,389
Cost | Office and lab equipment
Property, plant and equipment
Property, plant and equipment at beginning of period		2,389	2,112
Sales and disposals		(47)	(69)
Property, plant and equipment at end of period	3,477	2,712	2,389
Cost | Buildings
Property, plant and equipment
Property, plant and equipment at end of period	6,891
Cost | Vehicles
Property, plant and equipment
Property, plant and equipment at end of period	977
Cost | Leasehold improvements
Property, plant and equipment
Property, plant and equipment at end of period	808
Cost | Lease equipment
Property, plant and equipment
Property, plant and equipment at end of period	282	253
Accumulated depreciation and amortization
Property, plant and equipment
Property, plant and equipment at beginning of period		(1,713)	(1,346)
Depreciation		(46)	(58)
Property, plant and equipment at end of period	(4,269)	(2,141)	(1,713)
Accumulated depreciation and amortization | Office and lab equipment
Property, plant and equipment
Property, plant and equipment at beginning of period		(1,713)	(1,346)
Depreciation		(46)	(58)
Property, plant and equipment at end of period	(2,590)	(2,130)	€ (1,713)
Accumulated depreciation and amortization | Buildings
Property, plant and equipment
Property, plant and equipment at end of period	(1,315)
Accumulated depreciation and amortization | Vehicles
Property, plant and equipment
Property, plant and equipment at end of period	(233)
Accumulated depreciation and amortization | Leasehold improvements
Property, plant and equipment
Property, plant and equipment at end of period	(92)
Accumulated depreciation and amortization | Lease equipment
Property, plant and equipment
Property, plant and equipment at end of period	€ (39)	€ (11)

Financial assets - non-current

Financial assets - non-current (Details) - EUR (€) € in Millions	Oct. 31, 2019	Mar. 31, 2019
Financial assets - noncurrent
Secured Series A Financing	€ 1.1	€ 21

Research and development ince_3

Research and development incentive receivables (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Research and development incentive receivables
Research and development incentive receivables - Current	€ 261	€ 301	€ 158
Research and development incentive receivables - non-current	8,566	4,883	3,033
Total	€ 8,827	€ 5,184	€ 3,191
Minimum refund period of research and development incentive receivables.	5 years	5 years

Restricted cash (Details)

Restricted cash (Details) - EUR (€) € in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted cash
Rental guarantees	€ 630	€ 251	€ 256
Total noncurrent	630	251	256
Escrow account less than 1 year		1,692	1,692
Total restricted cash	€ 630	€ 1,943	€ 1,948

Trade and other receivables (De

Trade and other receivables (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Trade and other receivables
VAT receivable	€ 1,121	€ 496	€ 317
Trade receivables	22,580	214	845
Other receivables	1,378	455	750
Interest receivable	2,081	556
VLAIO grant receivable	955	1,165	930
Total trade and other current receivables	28,115	2,886	2,842
Impairment loss recognised in profit or loss, trade receivables	100
Bad debt allowance	0	0
Trade receivables impaired	0	0
Government grant received from Flanders Innovation and Entrepreneurship Agency	2,289	€ 1,842	€ 422
Flanders Innovation and Entrepreneurship Agency
Trade and other receivables
Government grant received from Flanders Innovation and Entrepreneurship Agency	€ 0

Financial assets - current (Det

Financial assets - current (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other current financial assets
Financial assets — current	€ 1,004,539	€ 283,529	€ 168,907
Maturity Term	6 months

Cash and cash equivalents (Deta

Cash and cash equivalents (Details) - EUR (€) € in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and cash equivalents
Cash equivalents	€ 252,550	€ 217,626	€ 25,000
Cash and bank balances	78,732	63,414	165,867
Total cash and cash equivalents	€ 331,282	€ 281,040	€ 190,867	€ 89,897

Share Capital and share premi_3

Share Capital and share premium (Details)	Dec. 31, 2019EUR (€)shares	Nov. 08, 2019shares	Nov. 07, 2019€ / sharesshares	Nov. 07, 2019$ / sharesshares	Dec. 31, 2018EUR (€)shares	Sep. 18, 2018EUR (€)€ / sharesshares	Dec. 15, 2017EUR (€)shares	Dec. 14, 2017$ / sharesshares	Dec. 13, 2017shares	May 19, 2017EUR (€)shares	May 17, 2017$ / sharesshares	Dec. 31, 2019shares	Nov. 30, 2019shares	Oct. 31, 2019shares	Sep. 30, 2019shares	Aug. 31, 2019shares	Jul. 31, 2019shares	Jun. 30, 2019shares	May 31, 2019shares	Apr. 30, 2019shares	Mar. 31, 2019shares	Feb. 28, 2019shares	Jan. 31, 2019shares	Dec. 31, 2018shares	Nov. 30, 2018shares	Oct. 31, 2018shares	Sep. 30, 2018shares	Aug. 31, 2018shares	Jul. 31, 2018shares	Jun. 30, 2018shares	May 31, 2018shares	Apr. 30, 2018shares	Mar. 31, 2018shares	Jan. 31, 2018shares	Dec. 31, 2017shares	Nov. 30, 2017shares	Oct. 31, 2017shares	Sep. 30, 2017shares	Aug. 31, 2017shares	Dec. 31, 2019EUR (€)shares	Dec. 31, 2018shares	Dec. 31, 2017EUR (€)shares	Dec. 31, 2019€ / sharesshares	Dec. 31, 2018€ / sharesshares	Dec. 31, 2017€ / sharesshares	Jan. 01, 2017shares
Disclosure of classes of share capital [line items]
Number of shares outstanding	42,761,528				35,975,312							42,761,528											35,975,312	35,975,312										32,180,641	32,180,641					42,761,528	35,975,312	32,180,641	42,761,528	35,975,312	32,180,641	20,126,479
Number of shares outstanding at beginning of period																							35,975,312											32,180,641						35,975,312	32,180,641
New shares issued for private placement, initial public offering, public offering and underwriters' over-allotment option		600,000	4,000,000	4,000,000		3,475,000	666,000	666,000	4,440,000	879,750	5,865,000																5,913	2,300					113,075	111,727								5,106,000
Exercise of Options									4,440,000			22,180	16,714	611	5,730	8,710	56	66,965	35,054	13,729	73,005	13,393	163,170	30,531	9,768	556			469	5,393	5,900	34,039			75,230		1,400	15,000	5,000
Number of shares outstanding at end of period	42,761,528				35,975,312							42,761,528												35,975,312											32,180,641					42,761,528	35,975,312	32,180,641
Share price | (per share)						€ 86.50		$ 52			$ 17
Number of shares on conversion											1																													1
Gross proceeds from issue of shares | €						€ 255,700,000	€ 225,600,000			€ 102,100,000																														€ 502,200,000
Underwriter discounts and commissions, and offering expenses | €						14,800,000	14,300,000			9,600,000																														23,200,000
Expenses deducted from equity | €						14,700,000	14,100,000			8,900,000																														23,000,000
Net proceeds | €						€ 240,900,000	€ 211,300,000			€ 92,500,000																														€ 479,000,000
Number of share options issued																																								419,317	319,671
Par value per share | € / shares																																											€ 0.1	€ 0.1	€ 0.1
Accounting treatment of the share subscription agreement | €																																								€ (24,948,000)
Maximum authorized increase of then outstanding share capital (as a percent)	20.00%				20.00%																																					20.00%
Period of outstanding share capital					18 months																																					18 months
Maximum authorized increase in share capital | €	€ 760,110				€ 648,790																																					€ 537,852.60
Maximum authorized increase in number of shares	7,601,101				6,487,896																																					5,378,526
Number of shares covered by existing authorization	3,001,101				3,012,896																																					272,526
American Depositary Shares [Member]
Disclosure of classes of share capital [line items]
Share price | $ / shares				$ 121
IFRS Employee Stock Option [Member]
Disclosure of classes of share capital [line items]
Exercise of Options																																			203,412
Private placement (Sunflower)
Disclosure of classes of share capital [line items]
New shares issued for private placement, initial public offering, public offering and underwriters' over-allotment option																																				106,782
Share price | € / shares			€ 109.18
Private placement (Sunflower) | American Depositary Shares [Member]
Disclosure of classes of share capital [line items]
New shares issued for private placement, initial public offering, public offering and underwriters' over-allotment option			2,589,943	2,589,943
Public Offering | American Depositary Shares [Member]
Disclosure of classes of share capital [line items]
New shares issued for private placement, initial public offering, public offering and underwriters' over-allotment option			1,410,057	1,410,057
Underwriters' Over Allotment Option | American Depositary Shares [Member]
Disclosure of classes of share capital [line items]
New shares issued for private placement, initial public offering, public offering and underwriters' over-allotment option		600,000
Johnson & Johnson Innovation Inc
Disclosure of classes of share capital [line items]
Share subscription																							1,766,899																	1,766,899

Share-based payments (Details)

Share-based payments (Details)	Dec. 20, 2019Y	Nov. 25, 2019	May 17, 2017shares	Dec. 31, 2019EquityInstrumentsY€ / shares	Nov. 30, 2019Y€ / shares	Jun. 30, 2019Y€ / shares	Dec. 31, 2018EquityInstrumentsY€ / shares	Jun. 30, 2018Y€ / shares	Dec. 31, 2017EquityInstrumentsY€ / shares	Jun. 30, 2017Y€ / shares	Dec. 31, 2019EquityInstruments€ / sharesshares	Dec. 31, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares	Dec. 31, 2016EquityInstruments
Disclosure of terms and conditions of share-based payment arrangement [line items]
Options expired											0	0	0
Exercised											419,317	319,671	203,412
Forfeited											124,437	46,369	2,369
Number of shares on conversion | shares			1								1
Vesting period		36 months									24 months
Exercise price per stock options | € / shares				€ 135.75	€ 113.49	€ 113.49	€ 86.32	€ 80.82	€ 21.17	€ 18.41	€ 135.75	€ 86.32	€ 21.17
Outstanding stock options				4,358,069			3,536,651		2,862,216		4,358,069	3,536,651	2,862,216	2,293,636
Time period for beneficiaries to choose contractual term (in days)	60 days
Option life (in years) | Y				6.50	6.50	8.59	7.83	7.36	10	10
Tranche One
Disclosure of terms and conditions of share-based payment arrangement [line items]
Vesting percentage		25.00%									33.00%
Tranche Two
Disclosure of terms and conditions of share-based payment arrangement [line items]
Vesting percentage		2.80%									4.16%
Percentage of stock options granted		75.00%									67.00%
3.95 | 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 3.95							€ 3.95
Outstanding stock options				7,210			18,200		36,960		7,210	18,200	36,960
3.95 | 2021
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 3.95							€ 3.95
Outstanding stock options									2,850				2,850
3.95 | 2024
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 3.95							€ 3.95
Outstanding stock options				6,238			6,895		15,692		6,238	6,895	15,692
2.44 - Expiry date 2024 option 1 | 2024
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 2.44							€ 2.44
Outstanding stock options				211,769			294,400		314,593		211,769	294,400	314,593
2.44 - Expiry date 2024 option 2 | 2024
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 2.44							€ 2.44
Outstanding stock options				96,696			117,733		135,890		96,696	117,733	135,890
2.44 - Expiry date 2024 option 3 | 2024
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 2.44							€ 2.44
Outstanding stock options				6,000			26,970		83,820		6,000	26,970	83,820
2.44
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercised												3,566
7.17 | 2024
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 7.17							€ 7.17
Outstanding stock options				335,067			407,061		516,100		335,067	407,061	516,100
11.44 | 2025
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 11.44							€ 11.44
Outstanding stock options				39,000			39,000		39,000		39,000	39,000	39,000
10.34 | 2025
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 10.34							€ 10.34
Outstanding stock options				3,000			3,000		3,000		3,000	3,000	3,000
9.47 | 2025
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 9.47							€ 9.47
Outstanding stock options				185,832			226,323		235,514		185,832	226,323	235,514
11.38 | 2026
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 11.38							€ 11.38
Outstanding stock options				45,000			50,415		60,000		45,000	50,415	60,000
113.39 | 2019 | Tranche One
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 113.49							€ 113.49
Outstanding stock options				279,760							279,760
113.39 | 2019 | Tranche Two
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 113.49							€ 113.49
Outstanding stock options				19,800							19,800
113.39 | 2024
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 113.49							€ 113.49
Outstanding stock options				111,690							111,690
135.75 | 2024/2029
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 135.75							€ 135.75
Outstanding stock options				921,885							921,885
11.47 | 2026
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 11.47							€ 11.47
Outstanding stock options				219,791			257,616		282,310		219,791	257,616	282,310
14.13 | 2026
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 14.13							€ 14.13
Outstanding stock options				258,746			315,102		362,126		258,746	315,102	362,126
18.41 | 2027
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 18.41							€ 18.41
Outstanding stock options				108,613			114,019		120,536		108,613	114,019	120,536
21.17 | 2027
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 21.17							€ 21.17
Outstanding stock options				565,798			628,292		653,825		565,798	628,292	653,825
80.82 | 2023
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 80.82							€ 80.82
Outstanding stock options				94,100			94,600				94,100	94,600
80.82 | 2028
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 80.82							€ 80.82
Outstanding stock options				73,100			75,450				73,100	75,450
86.32 | 2023
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 86.32							€ 86.32
Outstanding stock options				366,260			369,760				366,260	369,760
86.32 | 2028
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price per stock options | € / shares				€ 86.32							€ 86.32
Outstanding stock options				402,714			491,815				402,714	491,815
Maximum
Disclosure of terms and conditions of share-based payment arrangement [line items]
Option life (in years) | Y	10
Minimum
Disclosure of terms and conditions of share-based payment arrangement [line items]
Option life (in years) | Y	5

Share-based payments - Rollforw

Share-based payments - Rollforward (Details)	1 Months Ended							12 Months Ended
	Dec. 31, 2019EquityInstruments€ / shares	Nov. 30, 2019EquityInstruments	Jun. 30, 2019EquityInstruments	Dec. 31, 2018EquityInstruments€ / shares	Jun. 30, 2018EquityInstruments	Dec. 31, 2017EquityInstruments€ / shares	Jun. 30, 2017EquityInstruments	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares
Number of stock options
Total options at beginning of year | EquityInstruments								3,536,651	2,862,216	2,293,636
Granted | EquityInstruments	921,885	19,800	423,487	861,575	178,900	653,825	120,536	1,365,172	1,040,475	774,361
Exercised | EquityInstruments								(419,317)	(319,671)	(203,412)
Forfeited | EquityInstruments								(124,437)	(46,369)	(2,369)
Total options at end of year | EquityInstruments	4,358,069			3,536,651		2,862,216		4,358,069	3,536,651	2,862,216
Exercisable | EquityInstruments	2,203,476			1,859,315		1,598,829		2,203,476	1,859,315	1,598,829
Weighted average exercise price
Beginning balance								€ 33.42	€ 11.54	€ 7.72
Granted								128.52	85.37	20.74
Exercised								11.35	7.02	3.46
Forfeited								88.92	30.44	12.52
Ending balance	€ 63.75			€ 33.42		€ 11.54		63.75	33.42	11.54
Exercisable	€ 22.59			€ 9.62		€ 6.80		22.59	9.62	6.80
Weighted average share price								€ 110.99	€ 66.93	€ 23.53
Weighted average remaining contractual life								7 years 3 months 7 days	7 years 9 months 26 days	8 years 11 days

Share-based payments - Range of

Share-based payments - Range of exercise price (Details)	12 Months Ended
	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares	Nov. 30, 2019€ / shares	Jun. 30, 2019€ / shares	Jun. 30, 2018€ / shares	Jun. 30, 2017€ / shares	Dec. 31, 2016EquityInstruments
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	€ 135.75	€ 86.32	€ 21.17	€ 113.49	€ 113.49	€ 80.82	€ 18.41
Number of share options outstanding in share-based payment arrangement | EquityInstruments	4,358,069	3,536,651	2,862,216					2,293,636
Weighted average remaining contractual life	7 years 3 months 7 days	7 years 9 months 26 days	8 years 11 days
2.44-3.95
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of share options outstanding in share-based payment arrangement | EquityInstruments	327,913
Weighted average remaining contractual life	3 years 11 months 12 days
7.17-9.47
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of share options outstanding in share-based payment arrangement | EquityInstruments	520,899
Weighted average remaining contractual life	5 years 3 months 26 days
10.34-14.13
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of share options outstanding in share-based payment arrangement | EquityInstruments	565,537
Weighted average remaining contractual life	6 years 7 months 2 days
18.41-21.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of share options outstanding in share-based payment arrangement | EquityInstruments	674,411
Weighted average remaining contractual life	7 years 10 months 17 days
80.82-86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of share options outstanding in share-based payment arrangement | EquityInstruments	936,174
Weighted average remaining contractual life	6 years 5 months 5 days
113.49-135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of share options outstanding in share-based payment arrangement | EquityInstruments	1,333,135
Weighted average remaining contractual life	9 years 4 months 28 days
Minimum | 2.44-3.95
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	€ 2.44
Minimum | 7.17-9.47
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	7.17
Minimum | 10.34-14.13
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	10.34
Minimum | 18.41-21.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	18.41
Minimum | 80.82-86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	80.82
Minimum | 113.49-135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	113.49
Maximum | 2.44-3.95
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	3.95
Maximum | 7.17-9.47
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	9.47
Maximum | 10.34-14.13
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	14.13
Maximum | 18.41-21.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	21.17
Maximum | 80.82-86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	86.32
Maximum | 113.49-135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price	€ 135.75

Share-based payments - Overview

Share-based payments - Overview (Details)	Dec. 20, 2019EUR (€)Y	Nov. 25, 2019	Dec. 31, 2019EUR (€)EquityInstrumentsY€ / shares	Nov. 30, 2019EUR (€)EquityInstrumentsY€ / shares	Jun. 30, 2019EUR (€)EquityInstrumentsY€ / shares	Dec. 31, 2018EUR (€)EquityInstrumentsY€ / shares	Jun. 30, 2018EUR (€)EquityInstrumentsY€ / shares	Dec. 31, 2017EUR (€)EquityInstrumentsY€ / shares	Jun. 30, 2017EUR (€)EquityInstrumentsY€ / shares	Dec. 31, 2019EUR (€)EquityInstruments€ / shares	Dec. 31, 2018EUR (€)EquityInstruments€ / shares	Dec. 31, 2017EUR (€)EquityInstruments€ / shares	Dec. 31, 2016EquityInstruments
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options granted | EquityInstruments			921,885	19,800	423,487	861,575	178,900	653,825	120,536	1,365,172	1,040,475	774,361
Average fair value of options			€ 65,720,000	€ 57,690,000	€ 63,450,000	€ 39.85	€ 32.12	€ 37.10	€ 7.90	€ 65,720,000	€ 39.85	€ 37.10
Share price | € / shares			€ 146.40	€ 126.40	€ 123.20	€ 82.20	€ 72	€ 53.50	€ 17.76
Exercise price | € / shares			€ 135.75	€ 113.49	€ 113.49	€ 86.32	€ 80.82	€ 21.17	€ 18.41	€ 135.75	€ 86.32	€ 21.17
Expected volatility			44.18%	44.14%	45.25%	46.19%	45.50%	36.10%	36.60%
Riskfree interest rate			0.03%	0.05%	0.07%	0.77%	0.72%	0.53%	0.61%
Total share based payment expense										€ 39,600,000	€ 19,200,000	€ 4,300,000
Vesting period		36 months								24 months
Average expected option life (in years) | Y			6.50	6.50	8.59	7.83	7.36	10	10
Number of share options outstanding in share-based payment arrangement | EquityInstruments			4,358,069			3,536,651		2,862,216		4,358,069	3,536,651	2,862,216	2,293,636
Time period for beneficiaries to choose contractual term (in days)	60 days
Total fair value of grant			€ 65,720,000	€ 57,690,000	€ 63,450,000	€ 39.85	€ 32.12	€ 37.10	€ 7.90	€ 65,720,000	€ 39.85	€ 37.10
Share options granted (as a percent)	100.00%
Expected dividend yield										0.00%
Maximum
Disclosure of terms and conditions of share-based payment arrangement [line items]
Average fair value of options	€ 60,600,000
Average expected option life (in years) | Y	10
Total fair value of grant	€ 60,600,000
Minimum
Disclosure of terms and conditions of share-based payment arrangement [line items]
Average fair value of options	€ 49,500,000
Average expected option life (in years) | Y	5
Total fair value of grant	€ 49,500,000

Provisions for employee benefit

Provisions for employee benefits (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of net defined benefit liability (asset) [line items]
Deficit / surplus () of funded obligations	€ 64	€ 7	€ 25
Net liability (asset)	64	7	25
Employer contributions	300	200	300
Defined benefit obligation
Disclosure of net defined benefit liability (asset) [line items]
Net liability (asset)	1,789	1,277	1,007	€ 670
Fair value of plan assets
Disclosure of net defined benefit liability (asset) [line items]
Net liability (asset)	€ 1,725	€ 1,270	€ 982	€ 669
Belgium
Disclosure of net defined benefit liability (asset) [line items]
Guaranteed rate of return on employer contributions	3.25%
Guaranteed rate of return on employee contributions	3.75%
Minimum | Belgium
Disclosure of net defined benefit liability (asset) [line items]
Guaranteed rate of return on employer contributions	1.75%
Maximum | Belgium
Disclosure of net defined benefit liability (asset) [line items]
Guaranteed rate of return on employer contributions	3.75%

Provision for employee benefi_3

Provision for employee benefits - Rollforward (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	€ 7	€ 25
Ending balance	€ 64	€ 7	€ 25
Discount rate	1.00%	1.30%	1.30%
Term of Benefit Obligations	19 years 3 months 26 days
Weighted average age of the plan participants	46 years 2 months 12 days	43 years 9 months 18 days	46 years
Defined benefit obligation
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	€ 1,277	€ 1,007	€ 670
Service cost	379	336	352
Interest expense / income ()	19	15	11
Contributions by plan participants	(167)	(116)	(148)
Actuarial gains (+) / losses (-)	281	35	124
Benefits paid / transfers out			(2)
Ending balance	1,789	1,277	1,007
Fair value of plan assets
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	1,270	982	669
Interest expense / income ()	19	16	10
Administrative costs and taxes	(47)	(32)	(46)
Contributions by company & participants	475	328	423
Contributions by plan participants	(168)	(116)	(148)
Actuarial gains (+) / losses (-)	176	92	76
Benefits paid / transfers out			(2)
Ending balance	€ 1,725	€ 1,270	€ 982

Provision for employee benefi_4

Provision for employee benefits - Sensitivity Analysis (Details) - Discount rate	12 Months Ended
	Dec. 31, 2019EUR (€)
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Decrease in percentage	0.25%
Increase in percentage	0.25%
Defined benefit obligation increase due to increase in discount rate	€ 45,500
Defined benefit obligation decrease due to decrease in discount rate	€ (33,700)
Defined benefit obligation increase (in percentage)	2.54%
Defined benefit obligation decrease (in percentage)	1.88%

Trade and other payables (Detai

Trade and other payables (Details) - EUR (€) € in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of subsidiaries [line items]
Trade payables	€ 9,360	€ 6,007	€ 4,395
Accruals for invoices to be received	49,069	18,145	4,046
Short-term employee benefits accruals	26,872	€ 12,920	€ 6,844
Clinical Manufacturing Organizations
Disclosure of subsidiaries [line items]
Accruals for invoices to be received	€ 44,000

Tax liabilities (Details)

Tax liabilities (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of subsidiaries [line items]
Current tax liabilities, current	€ 344	€ 823	€ 597
Deferred tax asset recognized	160,000	€ 117,100
ARGENX BVBA
Disclosure of subsidiaries [line items]
Current tax liabilities, current	300
Additional tax deductible costs	€ 79,900

Revenue (Details)

Revenue (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue
Upfront payments	€ 22,360	€ 8,635	€ 20,137
Milestone payments	28,085	11,440	9,677
Research and development service fees (FTE)	19,338	1,407	6,601
Total revenue	€ 69,783	€ 21,482	€ 36,415

Revenue - Additional Informatio

Revenue - Additional Information (Details) € / shares in Units, $ / shares in Units, € in Thousands, $ in Millions	Sep. 18, 2018€ / shares	Dec. 14, 2017$ / shares	May 17, 2017$ / shares	Aug. 31, 2018USD ($)	Apr. 30, 2016EUR (€)item	Apr. 30, 2016USD ($)item	Dec. 31, 2019EUR (€)	Dec. 31, 2018EUR (€)	Dec. 31, 2018EUR (€)€ / sharesshares	Dec. 31, 2018USD ($)shares	Dec. 31, 2017EUR (€)	Dec. 31, 2018USD ($)	Jan. 01, 2018EUR (€)
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue							€ 69,783		€ 21,482		€ 36,415
Upfront payments							22,360		8,635		20,137
Research and development service fees (FTE)							19,338		1,407		6,601
Milestone payments							28,085		11,440		9,677
Deferred revenue - current							72,338	€ 2,161	2,161		8,635		€ 10,907
Deferred revenue - non-current							218,032				1,435		€ 1,813
Increase in research and development service fees							19,300		17,900
Amount of preclinical first milestone payment received | $				$ 30
Equity investment							678,936	255,721			€ 327,700
Share price | (per share)	€ 86.50	$ 52	$ 17
Collaboration and license agreement
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue							21,600
Deferred revenue								1,200	1,200
Unsatisfied performance obligations							€ 290,400	€ 2,200	2,200
Less than 1 year | Collaboration and license agreement
Disclosure of disaggregation of revenue from contracts with customers [line items]
Percentage of transaction price							25.00%
Later than one year and not later than six years | Collaboration and license agreement
Disclosure of disaggregation of revenue from contracts with customers [line items]
Percentage of transaction price							75.00%
AbbVie | Collaboration and license agreement
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue							€ 27,300
Upfront payments							800
Research and development service fees (FTE)							400
Milestone payments							26,100
Deferred revenue							1,400
Deferred revenue - current							1,200
Deferred revenue - non-current							200
Janssen | Collaboration and license agreement
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue							21,600
Upfront payments							18,300
Research and development service fees (FTE)							1,700
Milestone payments							1,600		€ 25,000
Deferred revenue							289,000
Deferred revenue - current							71,100
Deferred revenue - non-current							217,900
Milestone payment to be received							€ 1,300
Percentage share of royalties							50.00%
Upfront payment committed | $												$ 500
License payment committed | $												$ 300
Equity investment | $										$ 200
Shares issued | shares									1,766,899	1,766,899
Share price | € / shares									€ 100.02
AbbVie
Disclosure of disaggregation of revenue from contracts with customers [line items]
Upfront, non-refundable, non-creditable payment received					€ 35,100	$ 40
Maximum additional development milestone payments | $				110
Maximum additional regulatory milestone payments | $				$ 190
Term of additional GARP-related research funding				2 years
Maximum additional commercial milestone payments | $				$ 325
Amount of preclinical first milestone payment received					€ 8,900	$ 10
Number of preclinical milestones achieved | item					2	2
Amount of preclinical second milestone payment received					€ 8,700

Other operating income (Details

Other operating income (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other operating income
Grants	€ 2,289	€ 1,842	€ 422
Research and development incentives	4,818	2,151	983
Payroll tax rebates	5,694	3,756	3,436
Total	€ 12,801	€ 7,749	€ 4,841

Other operating income - Grants

Other operating income - Grants (Details) € in Thousands	Dec. 31, 2019EUR (€)item
Other operating income - Grants
Number of conditions related to government grants that are unfulfilled | item	0
Flanders Innovation & Entrepreneurship TGO
Other operating income - Grants
Amount granted and approved	€ 2,527
Amount recognized	845
Flanders Innovation & Entrepreneurship-Baekelandt
Other operating income - Grants
Amount granted and approved	2,634
Amount recognized	€ 1,411

Other operating income - Other

Other operating income - Other Incentives (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other operating income
Research and development incentives	€ 4,818	€ 2,151	€ 983
Incentive refund period	5 years
Payroll tax rebates	€ 5,694	€ 3,756	€ 3,436

Segment reporting (Details)

Segment reporting (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of geographical areas [line items]
Revenue from external customers	€ 69,783	€ 21,482	€ 36,415
Non-current assets	60,120	6,015	4,104
Netherlands
Disclosure of geographical areas [line items]
Revenue from external customers		470	628
Non-current assets	1	1	1
Belgium
Disclosure of geographical areas [line items]
Revenue from external customers	1,498
Non-current assets	56,777	5,967	4,103
Denmark
Disclosure of geographical areas [line items]
Revenue from external customers	436	1,136	6,240
Switzerland
Disclosure of geographical areas [line items]
Revenue from external customers	40,593	912	2,486
United States
Disclosure of geographical areas [line items]
Revenue from external customers			1
Non-current assets	3,058	47
Luxembourg
Disclosure of geographical areas [line items]
Revenue from external customers	€ 27,256	€ 18,964	€ 27,060

Segment reporting - Major clien

Segment reporting - Major clients (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment reporting - Major clients
Revenue	€ 69,783	€ 21,482	€ 36,415
Largest client
Segment reporting - Major clients
Revenue	40,600	19,000
Second largest client
Segment reporting - Major clients
Revenue	27,300	1,100
Third largest client
Segment reporting - Major clients
Revenue	€ 1,500	€ 900

Segment reporting - Noncurrent

Segment reporting - Noncurrent assets (Details) - EUR (€) € in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of geographical areas [line items]
Non-current assets	€ 60,120	€ 6,015	€ 4,104
Netherlands
Disclosure of geographical areas [line items]
Non-current assets	1	1	1
Belgium
Disclosure of geographical areas [line items]
Non-current assets	56,777	5,967	€ 4,103
United States
Disclosure of geographical areas [line items]
Non-current assets	3,058	€ 47
Japan
Disclosure of geographical areas [line items]
Non-current assets	€ 284

Research and development expe_3

Research and development expenses (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Research and development expenses
Personnel expenses	€ 45,733	€ 26,519	€ 16,473
External research and development expenses	137,050	48,859	27,893
Materials and consumables	2,027	1,464	1,562
Depreciation and amortisation	1,641	494	446
Other expenses	11,214	6,273	5,366
Research and development expenses	€ 197,665	€ 83,609	€ 51,740

Selling, general and administ_3

Selling, general and administrative expenses (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selling, general and administrative expenses
Personnel expenses	€ 40,082	€ 18,292	€ 6,745
Consulting fees	5,624	3,646	3,289
Marketing costs	10,719	1,826
Supervisory board	2,792	1,088	621
Office costs	5,352	2,619	1,793
Total	€ 64,569	€ 27,471	€ 12,448

Personnel expenses (Details)

Personnel expenses (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Personnel expenses
Short-term employee benefits - Salaries	€ 32,866	€ 18,617	€ 12,149
Short-term employee benefits - Social Security	3,555	2,213	1,504
Post-employment benefits	748	441	291
Termination benefits	644	96	8
Share-based payment	37,208	18,527	3,985
Employer social security contributions stock options	10,794	4,918	5,281
Total employee benefits expense	€ 85,815	€ 44,812	€ 23,218

Personnel expenses - FTE (Detai

Personnel expenses - FTE (Details) - employee	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Personnel expenses
Research and development	116.9	74.4	56.8
Selling, general and administrative	69.2	29.5	14.7
Number of FTE	186.1	103.9	71.5

Leases - Financial position rel

Leases - Financial position relating to leases (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	€ 6,564	€ 3,105
Additions to right-of-use assets	5,100
Lease liabilities
Lease liabilities — current	1,974	1,078
Lease liabilities — non-current	4,540	1,712
Lease liabilities	6,514	2,790
Buildings
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	5,576	2,338
Vehicles
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	744	525
Office and lab equipment
Disclosure of quantitative information about right-of-use assets [line items]
Right-of-use assets	€ 243	€ 242

Leases - Total contractual cash

Leases - Total contractual cash flow carrying amount (Details) - EUR (€) € in Thousands	Dec. 31, 2019	Jan. 01, 2019
Disclosure of maturity analysis of finance lease payments receivable [line items]
Total contractual cash flow	€ 7,025
Lease liabilities	6,514	€ 2,790
Less than 1 year
Disclosure of maturity analysis of finance lease payments receivable [line items]
Total contractual cash flow	2,205
1-3 years
Disclosure of maturity analysis of finance lease payments receivable [line items]
Total contractual cash flow	3,137
3-5 years
Disclosure of maturity analysis of finance lease payments receivable [line items]
Total contractual cash flow	1,251
More than 5 years
Disclosure of maturity analysis of finance lease payments receivable [line items]
Total contractual cash flow	€ 432

Leases - Statement of profit or

Leases - Statement of profit or loss and other comprehensive income (Details) - EUR (€) € in Thousands	Jan. 01, 2019	Dec. 31, 2019	Dec. 31, 2018
Financial position relating to leases
Depreciation, right-of-use assets		€ 1,576	€ 11
Interest expense (included in finance cost)		105
Expense relating to short-term leases	€ 88	123
Expense relating to leases of low-value assets that are not shown above as short-term leases		5
Cash outflow for leases		1,600
Buildings
Financial position relating to leases
Depreciation, right-of-use assets		1,315
Vehicles
Financial position relating to leases
Depreciation, right-of-use assets		233
Lease equipment
Financial position relating to leases
Depreciation, right-of-use assets		€ 28	€ 11

Leases - Additional information

Leases - Additional information (Details) € in Millions, ¥ in Millions	1 Months Ended		12 Months Ended
	Jan. 31, 2020CNY (¥)	Jan. 31, 2020EUR (€)	Dec. 31, 2019EUR (€)
Disclosure of quantitative information about right-of-use assets [line items]
Cash outflow for leases			€ 1.6
Office and laboratory space in Zwijnaarde, Belgium
Disclosure of quantitative information about right-of-use assets [line items]
Lease extension term			3 years
Office space in Boston, Massachusetts
Disclosure of quantitative information about right-of-use assets [line items]
Lease extension term			5 years
Office space in Tokyo, Japan
Disclosure of quantitative information about right-of-use assets [line items]
Cash outflow for leases	¥ 233.5	€ 1.9
Minimum | Office space in Tokyo, Japan
Disclosure of quantitative information about right-of-use assets [line items]
Lease term	3 years 2 months	3 years 2 months

Financial result and exchange_3

Financial result and exchange gains/(losses) (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financial result and exchange gains/(losses)
Interest income on bank deposits	€ 7,874	€ 1,371	€ 165
Net gains on current financial assets at FVTPL	6,525	2,323	210
Realized gain on non-current financial assets			875
Finance income	14,399	3,694	1,250
Financial expense	(124)
Realized exchange gains/(losses)	(338)	1,355
Unrealized exchange gains/(losses)	6,404	10,953	(5,797)
Exchange gains/(losses)	€ 6,066	€ 12,308	€ (5,797)

Income tax expense (Details)

Income tax expense (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income tax expense recognized
Loss before taxes	€ (158,213)	€ (65,847)	€ (27,479)
Income tax calculated at 25%	(39,553)	(16,462)	(6,870)
Effect of expenses that are not deductible in determining taxable results	(7,701)	(3,934)	(1,141)
Effect of stock issue expenses that are not deductible in determining taxable results	(5,750)	(3,716)	(5,754)
Effect of concessions (R&D incentives and grants)	(572)	(430)	(453)
Effect of different tax rates in jurisdictions in which the company operates	(52)	(15)	(517)
Deferred tax asset other than loss carryforwards not recognized	(27,341)	(11,968)	(4,363)
Other	13	26	9
Income tax expense recognized in the consolidated statement of profit and loss	(4,752)	(794)	(597)
Netherlands
Income tax expense recognized
Effect of tax losses carried forward not recognized	(356)
Effect of usage of tax losses carried forward not previously recognized			19,378
Belgium
Income tax expense recognized
Effect of tax losses carried forward not recognized	(11,314)	€ (5,511)	(27,413)
Effect of usage of tax losses carried forward not previously recognized	€ (3,876)
Effect of change in corporate tax rate on deferred tax asset not previously recognized (Belgium)			€ 373

Income tax expense - Deferred t

Income tax expense - Deferred tax assets (Details) - EUR (€) € in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income tax expense - Deferred tax assets
Unused tax losses for which no deferred tax asset recognised	€ 160	€ 117.1
Unused tax loss carried forward, which will expire in 2028	€ 1.4
Tax rate applicable	25.00%	25.00%	25.00%
Temporary differences and unused tax losses
Income tax expense - Deferred tax assets
Unrecognized deferred tax assets	€ 40	€ 29.3
Netherlands
Income tax expense - Deferred tax assets
Tax rate applicable	25.00%	25.00%	25.00%
Belgium
Income tax expense - Deferred tax assets
Tax rate applicable	25.00%

Income tax expense - Restructur

Income tax expense - Restructuring (Details) € in Millions	12 Months Ended
	Dec. 31, 2019EUR (€)
ARGENX BVBA
Restructuring
Additional tax deductible costs	€ 79.9

Loss per share (Details)

Loss per share (Details) - EUR (€) € / shares in Units, € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loss per share
Loss of the year	€ (162,965)	€ (66,641)	€ (28,076)
Weighted average number of shares outstanding	38,619,121	33,419,356	24,609,536
Basic and diluted loss per share	€ (4.22)	€ (1.99)	€ (1.14)
Other instruments that could potentially dilute earnings per ordinary share in the future	0

Financial instruments and fin_3

Financial instruments and financial risk management (Details) - EUR (€) € in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financial assets — non-current
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39		€ 1
Carrying amount of assets under IFRS 9			€ 1
Amortised cost | Trade and other payables
Disclosure of financial assets [line items]
Carrying amount of liabilities under IAS 39	€ 85,301	37,072
Carrying amount of liabilities under IFRS 9			15,285
Available for sale | Financial assets — non-current
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39	2,596
FVTPL | Financial assets—current
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39	1,004,539	283,529
Carrying amount of assets under IFRS 9			168,907
Amortised cost | Research and development incentive receivables — non-current member
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39	8,566	4,883
Carrying amount of assets under IFRS 9			3,033
Amortised cost | Restricted cash — non-current
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39	630	251
Carrying amount of assets under IFRS 9			256
Amortised cost | Trade and other receivables
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39	28,115	2,886
Carrying amount of assets under IFRS 9			2,842
Amortised cost | Prepaid expenses
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39	9,022	2,995
Carrying amount of assets under IFRS 9			2,338
Amortised cost | Research and development incentive receivables — current
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39	261	301
Carrying amount of assets under IFRS 9			158
Amortised cost | Restricted cash — current
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39		1,692
Carrying amount of assets under IFRS 9			1,692
Amortised cost | Cash and cash equivalents
Disclosure of financial assets [line items]
Carrying amount of assets under IAS 39	€ 331,282	€ 281,040
Carrying amount of assets under IFRS 9			€ 190,867

Financial instruments and fin_4

Financial instruments and financial risk management - Fair value (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair value hierarchy
Transfers out of Level 1 to Level 2 assets	€ 0
Transfers out of Level 1 to Level 2 liabilities	0
Transfers out of Level 2 to Level 1 assets	0
Transfers out of Level 2 to Level 1 liabilities	0
Transfer into level 3 assets	0
Transfer out of level 3 assets	0
Transfer into level 3 liabilities	0
Transfer out of level 3 liabilities	0
Level 1
Fair value hierarchy
Current financial assets	1,004,539	€ 283,529	€ 168,907
Assets carried at fair value	1,004,539	283,529	168,907
Level 3
Fair value hierarchy
Non-current financial assets	2,596	1	1
Assets carried at fair value	€ 2,596	€ 1	€ 1

Financial instruments and fin_5

Financial instruments and financial risk management - Capital risk (Details) - EUR (€) € in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financial instruments and financial risk management
Cash and cash equivalents	€ 331,282	€ 281,040	€ 190,867	€ 89,897
Total capital	€ 1,312,800

Financial instruments and fin_6

Financial instruments and financial risk management - Credit risk (Details) - Credit risk € in Thousands	12 Months Ended
	Dec. 31, 2019EUR (€)
Financial assets past due but not impaired
Disclosure of financial assets that are either past due or impaired [line items]
Financial assets	€ 0
Financial assets impaired
Disclosure of financial assets that are either past due or impaired [line items]
Financial assets	€ 0
Maximum
Disclosure of financial assets that are either past due or impaired [line items]
Recommended maturity term for short term investment	6 months

Financial instruments and fin_7

Financial instruments and financial risk management - Interest rate risk (Details) - Interest rate risk - EUR (€) € in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of risk management strategy related to hedge accounting [line items]
Increase decrease in basis points	0.25%
Positive/negative impact	€ 2	€ 0.3	€ 0.3

Financial instruments and fin_8

Financial instruments and financial risk management - Foreign exchange risk (Details) - Currency risk - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
USD
Disclosure of risk management strategy related to hedge accounting [line items]
Net exposure to exchange differences of the monetary assets	€ 821,916	€ 312,831	€ 147,169
Percentage of reasonably possible increase in risk assumption	10.00%	10.00%
Percent of reasonably possible decrease in risk assumption	10.00%	10.00%
Increase (decrease) in financial instrument due to reasonably possible increase in designated risk component	€ (74,720)	€ (28,440)
Increase (decrease) in financial instrument due to reasonably possible decrease in designated risk component	74,720	28,440
JPY
Disclosure of risk management strategy related to hedge accounting [line items]
Net exposure to exchange differences of the monetary assets	488
GBP
Disclosure of risk management strategy related to hedge accounting [line items]
Net exposure to exchange differences of the monetary assets	4	2	406
CHF
Disclosure of risk management strategy related to hedge accounting [line items]
Net exposure to exchange differences of the monetary assets	€ 1	€ 4	€ 25
Other currencies
Disclosure of risk management strategy related to hedge accounting [line items]
Percentage of reasonably possible increase in risk assumption	10.00%
Percent of reasonably possible decrease in risk assumption	10.00%
Increase (decrease) in financial instrument due to reasonably possible increase in designated risk component	€ 0
Increase (decrease) in financial instrument due to reasonably possible decrease in designated risk component	€ 0

Related party transactions - Co

Related party transactions - Compensation (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Compensation of key management personnel
Short term employee benefits	€ 4,437	€ 4,236	€ 3,126
Post employment benefits	144	153	115
Termination benefits	470
Sharebased payment	21,847	13,363	12,041
Employer social security contributions stock options	9,160	2,792	3,073
Total	36,058	20,544	18,355
Expense from share-based payment transactions with employees	39,600	19,200	4,300
Key management personnel of entity or parent [member]
Compensation of key management personnel
Expense from share-based payment transactions with employees	€ 14,400	€ 10,700	€ 2,300

Related party transactions - Ex

Related party transactions - Executive directors remuneration (Details) - EUR (€)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of transactions between related parties [line items]
Pension contribution	€ 144,000	€ 153,000	€ 115,000
Social security costs	9,160,000	2,792,000	3,073,000
ESOP	21,847,000	13,363,000	12,041,000
Total	36,058,000	20,544,000	18,355,000
Executive Directors
Disclosure of transactions between related parties [line items]
Base salary	525,000	500,000	575,285
Bonus	326,288	284,600	474,919
Pension contribution	21,532	15,102	76,650
Social security costs	10,587	10,011	264,191
ESOP	5,257,360	3,559,200	7,057,404
Other	11,558	33,855	24,580
Total	6,152,325	4,402,768	8,473,029
Tim Van Hauwermeiren
Disclosure of transactions between related parties [line items]
Base salary	525,000	500,000	303,941
Bonus	326,288	284,600	301,635
Pension contribution	21,532	15,102	14,315
Social security costs	10,587	10,011	9,459
ESOP	5,257,360	3,559,200	2,968,195
Other	11,558	33,855	9,601
Total	€ 6,152,325	€ 4,402,768	3,607,146
Eric Castaldi
Disclosure of transactions between related parties [line items]
Base salary			271,344
Bonus			173,284
Pension contribution			62,335
Social security costs			254,732
ESOP			4,089,209
Other			14,979
Total			€ 4,865,883

Related party transactions - _2

Related party transactions - Executive directors ESOP (Details)	Dec. 20, 2019	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares	Nov. 30, 2019€ / shares	Jun. 30, 2019€ / shares	Jan. 01, 2019EquityInstruments	Jun. 30, 2018€ / shares	Jun. 30, 2017€ / shares	Dec. 31, 2016EquityInstruments
Disclosure of terms and conditions of share-based payment arrangement [line items]
Outstanding stock options		4,358,069	3,536,651	2,862,216						2,293,636
Exercise price | € / shares		€ 135.75	€ 86.32	€ 21.17	€ 113.49	€ 113.49		€ 80.82	€ 18.41
Exercised		419,317	319,671	203,412
Time period for beneficiaries to choose contractual term (in days)	60 days
2.44
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercised			3,566
Executive Directors
Disclosure of terms and conditions of share-based payment arrangement [line items]
Outstanding stock options		80,000	80,000	123,200
Exercised		30,000	40,000	65,380
Tim Van Hauwermeiren | 2.44
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares				€ 2.44
Exercised				65,380
Tim Van Hauwermeiren | 21.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Outstanding stock options				80,000
Term				10 years
Exercise price | € / shares				€ 21.17
Tim Van Hauwermeiren | 86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Outstanding stock options			80,000
Term		10 years	10 years
Exercise price | € / shares			€ 86.32
Tim Van Hauwermeiren | 135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Outstanding stock options		80,000
Exercise price | € / shares		€ 135.75
Tim Van Hauwermeiren | 7.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Outstanding stock options		386,200					336,200
Exercise price | € / shares		€ 7.17	€ 7.17
Exercised		30,000	40,000
Eric Castaldi | 21.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Outstanding stock options				43,200
Term				10 years
Exercise price | € / shares				€ 21.17

Related party transactions - _3

Related party transactions - Executive directors ESOP - Rollforward and Vesting (Details)	1 Months Ended							12 Months Ended
	Dec. 31, 2019EquityInstruments€ / shares	Nov. 30, 2019EquityInstruments€ / shares	Jun. 30, 2019EquityInstruments€ / shares	Dec. 31, 2018EquityInstruments€ / shares	Jun. 30, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares	Jun. 30, 2017EquityInstruments€ / shares	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								3,536,651		2,862,216	2,293,636
Granted	921,885	19,800	423,487	861,575	178,900	653,825	120,536	1,365,172		1,040,475	774,361
Exercised								(419,317)		(319,671)	(203,412)
Total options at end of year	4,358,069			3,536,651		2,862,216		4,358,069	4,358,069	3,536,651	2,862,216
Exercise price | € / shares	€ 135.75	€ 113.49	€ 113.49	€ 86.32	€ 80.82	€ 21.17	€ 18.41	€ 135.75	€ 135.75	€ 86.32	€ 21.17
135.75 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
135.75 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
135.75 | Options to vest in 2021
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
86.32 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,667							26,667	26,667
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,666							26,666	26,666
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,667							26,667	26,667
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
Tim Van Hauwermeiren | 7.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									336,200
Granted								80,000
Exercised								(30,000)		(40,000)
Total options at end of year	386,200							386,200	386,200
Exercise price | € / shares	€ 7.17			€ 7.17				€ 7.17	€ 7.17	€ 7.17
Tim Van Hauwermeiren | 7.17 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	35,000							35,000	35,000
Exercise price | € / shares	€ 7.17							€ 7.17	€ 7.17
Tim Van Hauwermeiren | 9.47 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	30,600							30,600	30,600
Exercise price | € / shares	€ 9.47							€ 9.47	€ 9.47
Tim Van Hauwermeiren | 9.47 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	€ 9.47							€ 9.47	€ 9.47
Tim Van Hauwermeiren | 11.47 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	43,056							43,056	43,056
Exercise price | € / shares	€ 11.47							€ 11.47	€ 11.47
Tim Van Hauwermeiren | 11.47 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	6,944							6,944	6,944
Exercise price | € / shares	€ 11.47							€ 11.47	€ 11.47
Tim Van Hauwermeiren | 11.47 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	€ 11.47							€ 11.47	€ 11.47
Tim Van Hauwermeiren | 135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	80,000							80,000	80,000
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Tim Van Hauwermeiren | 135.75 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,667							26,667	26,667
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Tim Van Hauwermeiren | 135.75 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,666							26,666	26,666
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Tim Van Hauwermeiren | 135.75 | Options to vest in 2021
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,667							26,667	26,667
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Tim Van Hauwermeiren | 14.13 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	20,400							20,400	20,400
Exercise price | € / shares	€ 14.13							€ 14.13	€ 14.13
Tim Van Hauwermeiren | 14.13 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	10,200							10,200	10,200
Exercise price | € / shares	€ 14.13							€ 14.13	€ 14.13
Tim Van Hauwermeiren | 14.13 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	€ 14.13							€ 14.13	€ 14.13
Tim Van Hauwermeiren | 21.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year										80,000
Total options at end of year						80,000					80,000
Exercise price | € / shares						€ 21.17					€ 21.17
Tim Van Hauwermeiren | 21.17 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,667							26,667	26,667
Exercise price | € / shares	€ 21.17							€ 21.17	€ 21.17
Tim Van Hauwermeiren | 21.17 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,666							26,666	26,666
Exercise price | € / shares	€ 21.17							€ 21.17	€ 21.17
Tim Van Hauwermeiren | 21.17 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,667							26,667	26,667
Exercise price | € / shares	€ 21.17							€ 21.17	€ 21.17
Tim Van Hauwermeiren | 21.17 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	€ 21.17							€ 21.17	€ 21.17
Tim Van Hauwermeiren | 86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								80,000
Total options at end of year				80,000						80,000
Exercise price | € / shares				€ 86.32						€ 86.32
Eric Castaldi | 21.17
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year										43,200
Total options at end of year						43,200					43,200
Exercise price | € / shares						€ 21.17					€ 21.17
A.A. Rosenberg | 135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	10,000							10,000	10,000
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
A.A. Rosenberg | 135.75 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
A.A. Rosenberg | 135.75 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
A.A. Rosenberg | 135.75 | Options to vest in 2021
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
A.A. Rosenberg | 86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
A.A. Rosenberg | 86.32 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
A.A. Rosenberg | 86.32 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
A.A. Rosenberg | 86.32 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
J. Donald deBethizy | 11.44
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									35,000
Granted									10,000
Total options at end of year	45,000							45,000	45,000
J. Donald deBethizy | 11.44 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	15,000							15,000	15,000
Exercise price | € / shares	€ 11.44							€ 11.44	€ 11.44
J. Donald deBethizy | 135.75 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
J. Donald deBethizy | 135.75 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
J. Donald deBethizy | 135.75 | Options to vest in 2021
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
J. Donald deBethizy | 86.32 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
J. Donald deBethizy | 86.32 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
J. Donald deBethizy | 86.32 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
James M Daly | 135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	10,000							10,000	10,000
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
James M Daly | 135.75 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
James M Daly | 135.75 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
James M Daly | 135.75 | Options to vest in 2021
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
James M Daly | 86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
James M Daly | 86.32 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
James M Daly | 86.32 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
James M Daly | 86.32 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
Pamela Klein | 11.44
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									35,000
Granted									10,000
Total options at end of year	45,000							45,000	45,000
Pamela Klein | 11.44 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	15,000							15,000	15,000
Exercise price | € / shares	€ 11.44							€ 11.44	€ 11.44
Pamela Klein | 135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	10,000							10,000	10,000
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Pamela Klein | 135.75 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Pamela Klein | 135.75 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Pamela Klein | 135.75 | Options to vest in 2021
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Pamela Klein | 14.13
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									25,000
Granted									10,000
Total options at end of year	35,000							35,000	35,000
Pamela Klein | 14.13 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	10,000							10,000	10,000
Exercise price | € / shares	€ 14.13							€ 14.13	€ 14.13
Pamela Klein | 14.13 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	5,000							5,000	5,000
Exercise price | € / shares	€ 14.13							€ 14.13	€ 14.13
Pamela Klein | 86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
Pamela Klein | 86.32 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
Pamela Klein | 86.32 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
Pamela Klein | 86.32 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
Peter Verhaeghe | 7.17 | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	5,000							5,000	5,000
Exercise price | € / shares	€ 7.17							€ 7.17	€ 7.17
Peter Verhaeghe | 135.75
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	10,000							10,000	10,000
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Peter Verhaeghe | 135.75 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Peter Verhaeghe | 135.75 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Peter Verhaeghe | 135.75 | Options to vest in 2021
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 135.75							€ 135.75	€ 135.75
Peter Verhaeghe | 86.32
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
Peter Verhaeghe | 86.32 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
Peter Verhaeghe | 86.32 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
Peter Verhaeghe | 86.32 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32

Related party transactions - _4

Related party transactions - Executive directors ESOP - Remaining term (Details) - EquityInstruments	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	4,358,069	3,536,651	2,862,216	2,293,636
Remaining term	7 years 3 months 7 days	7 years 9 months 26 days	8 years 11 days
9.0 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	80,000
Tim Van Hauwermeiren | 5.0 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	35,000
Remaining term	5 years
Tim Van Hauwermeiren | 5.0 years | Minimum
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Remaining term	10 years
Tim Van Hauwermeiren | 6.0 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	30,600
Remaining term	6 years
Tim Van Hauwermeiren | 6.5 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	50,000
Remaining term	6 years 6 months
Tim Van Hauwermeiren | 7.0 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	30,600
Remaining term	7 years
Tim Van Hauwermeiren | 8.0 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	80,000
Remaining term	8 years
Tim Van Hauwermeiren | 9.0 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Remaining term	9 years
Tim Van Hauwermeiren | 10.0 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	80,000
Remaining term	10 years

Related party transactions - Re

Related party transactions - Remuneration of non-executive directors (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	€ 36,058	€ 20,544	€ 18,355
Non-executive Directors
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	377,500	355,000	320,000
Peter Verhaeghe
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	77,500	77,500	77,500
David L Lacey
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	50,000	50,000	50,000
Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	55,000	55,000	55,000
Pamela Klein
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	42,500	42,500	42,500
Don Debethizy
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	52,500	52,500	52,500
A.A. Rosenberg
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	50,000	42,500	€ 42,500
James M Daly
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total	€ 50,000	€ 35,000

Related party transactions - No

Related party transactions - Non-executive directors ESOP (Details)	12 Months Ended
	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares	Nov. 30, 2019€ / shares	Jun. 30, 2019€ / shares	Jan. 01, 2019EquityInstruments	Jun. 30, 2018€ / shares	Jun. 30, 2017€ / shares	Dec. 31, 2016EquityInstruments
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	4,358,069	4,358,069	3,536,651	2,862,216						2,293,636
Exercise price | € / shares	€ 135.75	€ 135.75	€ 86.32	€ 21.17	€ 113.49	€ 113.49		€ 80.82	€ 18.41
Exercised	419,317		319,671	203,412
Non-executive Directors
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	70,000	70,000	85,000	15,000
Exercised	4,444		24,972
21.37 | David L Lacey
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options				15,000
Term				10 years
Exercise price | € / shares				€ 21.37
86.32 | Peter Verhaeghe
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options			10,000
Term			10 years
Exercise price | € / shares			€ 86.32
86.32 | David L Lacey
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options			10,000
Term			10 years
Exercise price | € / shares			€ 86.32
86.32 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options			10,000
Term			10 years
Exercise price | € / shares			€ 86.32
86.32 | Don Debethizy
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options			10,000
Term			10 years
Exercise price | € / shares			€ 86.32
86.32 | Pamela Klein
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options			10,000
Term			10 years
Exercise price | € / shares			€ 86.32
86.32 | A.A. Rosenberg
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options			10,000
Term			10 years
Exercise price | € / shares			€ 86.32
86.32 | James M Daly
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options			10,000
Term			10 years
Exercise price | € / shares			€ 86.32
2.44
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercised			3,566
2.44 | Peter Verhaeghe
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	54,585	54,585					44,585
2.44 | David L Lacey
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	64,443	64,443					54,443
2.44 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	20,000	20,000					14,444
Exercise price | € / shares			€ 2.44
Exercised		4,444	10,850
135.75 | Peter Verhaeghe
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	10,000	10,000
Term	10 years
Exercise price | € / shares	€ 135.75	€ 135.75
135.75 | David L Lacey
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	10,000	10,000
Term	10 years
Exercise price | € / shares	€ 135.75	€ 135.75
135.75 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	10,000	10,000
Term	10 years
Exercise price | € / shares	€ 135.75	€ 135.75
135.75 | Don Debethizy
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	10,000	10,000
Term	10 years
Exercise price | € / shares	€ 135.75	€ 135.75
135.75 | Pamela Klein
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	10,000	10,000
Term	10 years
Exercise price | € / shares	€ 135.75	€ 135.75
135.75 | A.A. Rosenberg
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	10,000	10,000
Term	10 years
Exercise price | € / shares	€ 135.75	€ 135.75
135.75 | James M Daly
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	10,000	10,000
Term	10 years
Exercise price | € / shares	€ 135.75	€ 135.75
7.17 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares			€ 7.17
Exercised			5,000
80.82 | James M Daly
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options	35,000	35,000	15,000				25,000
Term			10 years
Exercise price | € / shares			€ 80.82
11.38 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	€ 11.38	€ 11.38	€ 11.38
Exercised	4,444		5,556

Related party transactions - _5

Related party transactions - Non-executive directors ESOP - Rollforward and vesting (Details)	1 Months Ended							12 Months Ended
	Dec. 31, 2019EquityInstruments€ / shares	Nov. 30, 2019EquityInstruments€ / shares	Jun. 30, 2019EquityInstruments€ / shares	Dec. 31, 2018EquityInstruments€ / shares	Jun. 30, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares	Jun. 30, 2017EquityInstruments€ / shares	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2019EquityInstruments€ / shares	Dec. 31, 2018EquityInstruments€ / shares	Dec. 31, 2017EquityInstruments€ / shares
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								3,536,651		2,862,216	2,293,636
Number of options granted	921,885	19,800	423,487	861,575	178,900	653,825	120,536	1,365,172		1,040,475	774,361
Exercised								(419,317)		(319,671)	(203,412)
Total options at end of year	4,358,069			3,536,651		2,862,216		4,358,069	4,358,069	3,536,651	2,862,216
Exercise price | € / shares	€ 135.75	€ 113.49	€ 113.49	€ 86.32	€ 80.82	€ 21.17	€ 18.41	€ 135.75	€ 135.75	€ 86.32	€ 21.17
2.44
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercised										(3,566)
2.44 | Peter Verhaeghe
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									44,585
Number of options granted									10,000
Total options at end of year	54,585							54,585	54,585
2.44 | Peter Verhaeghe | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	11,626							11,626	11,626
Exercise price | € / shares	€ 2.44							€ 2.44	€ 2.44
2.44 | David L Lacey
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									54,443
Number of options granted									10,000
Total options at end of year	64,443							64,443	64,443
2.44 | David L Lacey | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	6,643							6,643	6,643
Exercise price | € / shares	€ 2.44							€ 2.44	€ 2.44
2.44 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									14,444
Number of options granted									10,000
Exercised									(4,444)	(10,850)
Total options at end of year	20,000							20,000	20,000
Exercise price | € / shares				2.44						€ 2.44
2.44 | Werner Lanthaler | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	€ 2.44							€ 2.44	€ 2.44
3.95 | Peter Verhaeghe | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	7,959							7,959	7,959
Exercise price | € / shares	€ 3.95							€ 3.95	€ 3.95
7.17 | Peter Verhaeghe | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	5,000							5,000	5,000
Exercise price | € / shares	€ 7.17							€ 7.17	€ 7.17
7.17 | David L Lacey | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	12,800							12,800	12,800
Exercise price | € / shares	€ 7.17							€ 7.17	€ 7.17
7.17 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercised										(5,000)
Exercise price | € / shares				7.17						€ 7.17
7.17 | Werner Lanthaler | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	€ 7.17							€ 7.17	€ 7.17
11.38 | Peter Verhaeghe | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	8,333							8,333	8,333
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
11.38 | Peter Verhaeghe | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	1,667							1,667	1,667
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
11.38 | David L Lacey | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	8,333							8,333	8,333
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
11.38 | David L Lacey | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	1,667							1,667	1,667
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
11.38 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercised								(4,444)		(5,556)
Exercise price | € / shares	11.38			€ 11.38				€ 11.38	11.38	€ 11.38
11.38 | Werner Lanthaler | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	11.38							11.38	11.38
11.38 | Werner Lanthaler | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
11.38 | J. Donald deBethizy | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	8,333							8,333	8,333
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
11.38 | J. Donald deBethizy | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	1,667							1,667	1,667
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
11.38 | Pamela Klein | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	8,333							8,333	8,333
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
11.38 | Pamela Klein | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	1,667							1,667	1,667
Exercise price | € / shares	€ 11.38							€ 11.38	€ 11.38
86.32 | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,667							26,667	26,667
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,666							26,666	26,666
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	26,667							26,667	26,667
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Peter Verhaeghe
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
86.32 | Peter Verhaeghe | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Peter Verhaeghe | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Peter Verhaeghe | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | David L Lacey
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
86.32 | David L Lacey | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | David L Lacey | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | David L Lacey | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Werner Lanthaler
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
86.32 | Werner Lanthaler | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Werner Lanthaler | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Werner Lanthaler | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | J. Donald deBethizy | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | J. Donald deBethizy | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | J. Donald deBethizy | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Pamela Klein
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
86.32 | Pamela Klein | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Pamela Klein | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Pamela Klein | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | Don Debethizy
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
86.32 | A.A. Rosenberg
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
86.32 | A.A. Rosenberg | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | A.A. Rosenberg | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | A.A. Rosenberg | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | James M Daly
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								10,000
Total options at end of year				10,000						10,000
Exercise price | € / shares				€ 86.32						€ 86.32
86.32 | James M Daly | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | James M Daly | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,334							3,334	3,334
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
86.32 | James M Daly | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	3,333							3,333	3,333
Exercise price | € / shares	€ 86.32							€ 86.32	€ 86.32
21.17 | David L Lacey | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	5,000							5,000	5,000
Exercise price | € / shares	€ 21.17							€ 21.17	€ 21.17
21.17 | David L Lacey | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	5,000							5,000	5,000
Exercise price | € / shares	€ 21.17							€ 21.17	€ 21.17
21.17 | David L Lacey | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	5,000							5,000	5,000
Exercise price | € / shares	€ 21.17							€ 21.17	€ 21.17
11.44 | J. Donald deBethizy
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									35,000
Number of options granted									10,000
Total options at end of year	45,000							45,000	45,000
11.44 | J. Donald deBethizy | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	15,000							15,000	15,000
Exercise price | € / shares	€ 11.44							€ 11.44	€ 11.44
11.44 | Pamela Klein
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									35,000
Number of options granted									10,000
Total options at end of year	45,000							45,000	45,000
11.44 | Pamela Klein | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	15,000							15,000	15,000
Exercise price | € / shares	€ 11.44							€ 11.44	€ 11.44
14.13 | Pamela Klein
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year									25,000
Number of options granted									10,000
Total options at end of year	35,000							35,000	35,000
14.13 | Pamela Klein | Options vested until 2017
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	10,000							10,000	10,000
Exercise price | € / shares	€ 14.13							€ 14.13	€ 14.13
14.13 | Pamela Klein | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	5,000							5,000	5,000
Exercise price | € / shares	€ 14.13							€ 14.13	€ 14.13
80.82 | James M Daly
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at beginning of year								15,000	25,000
Number of options granted									10,000
Total options at end of year	35,000			15,000				35,000	35,000	15,000
Exercise price | € / shares				€ 80.82						€ 80.82
80.82 | James M Daly | Options vested in 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	7,500							7,500	7,500
Exercise price | € / shares	€ 80.82							€ 80.82	€ 80.82
80.82 | James M Daly | Options to vest in 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	5,000							5,000	5,000
Exercise price | € / shares	€ 80.82							€ 80.82	€ 80.82
80.82 | James M Daly | Options to vest in 2020
Disclosure of terms and conditions of share-based payment arrangement [line items]
Total options at end of year	2,500							2,500	2,500
Exercise price | € / shares	€ 80.82							€ 80.82	€ 80.82

Related party transactions - _6

Related party transactions - Non-executive directors ESOP - Remaining term (Details) - EquityInstruments	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	4,358,069	3,536,651	2,862,216	2,293,636
Remaining term	7 years 3 months 7 days	7 years 9 months 26 days	8 years 11 days
Exercise of Options	419,317	319,671	203,412
Non-executive Directors
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	70,000	85,000	15,000
Exercise of Options	4,444	24,972
1.0 years | Peter Verhaeghe
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	2,340
Remaining term	1 year
5.0 years | Peter Verhaeghe
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	9,854
Remaining term	5 years
5.0 years | David L Lacey
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	14,445
Remaining term	5 years
4.0 years | Peter Verhaeghe
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	3,181
Remaining term	4 years
4.0 years | David L Lacey
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	1,818
Remaining term	4 years
5.5 years | Werner Lanthaler
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Remaining term	5 years 6 months
5.5 years | J. Donald deBethizy
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	15,000
5.5 years | Don Debethizy
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Remaining term	5 years 6 months
5.5 years | Pamela Klein
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	15,000
3.5 years | Peter Verhaeghe
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	5,560
Remaining term	3 years 6 months
3.5 years | David L Lacey
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	3,180
Remaining term	3 years 6 months
0.5 years | Peter Verhaeghe
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	3,650
Remaining term	6 months
6.5 years | Peter Verhaeghe
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	6 years 6 months
6.5 years | David L Lacey
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	6 years 6 months
6.5 years | J. Donald deBethizy
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	6 years 6 months
6.5 years | Pamela Klein
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
7.0 years | Pamela Klein
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Remaining term	7 years
7.0 years | A.A. Rosenberg
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	15,000
8.0 years | David L Lacey
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	15,000
Remaining term	8 years
8.5 years | A.A. Rosenberg
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Remaining term	8 years 6 months
8.5 years | James M Daly
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	15,000
9.0 years
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	80,000
9.0 years | Peter Verhaeghe
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	9 years
9.0 years | David L Lacey
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	9 years
9.0 years | Werner Lanthaler
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	9 years
9.0 years | J. Donald deBethizy
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	9 years
9.0 years | Pamela Klein
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	9 years
9.0 years | A.A. Rosenberg
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	9 years
9.0 years | James M Daly
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	9 years
10.0 years | Peter Verhaeghe
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	10 years
10.0 years | David L Lacey
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	10 years
10.0 years | Werner Lanthaler
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	10 years
10.0 years | J. Donald deBethizy
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
10.0 years | Don Debethizy
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Remaining term	10 years
10.0 years | Pamela Klein
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	10 years
10.0 years | A.A. Rosenberg
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	10 years
10.0 years | James M Daly
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options	10,000
Remaining term	10 years

Contingencies (Details)

Contingencies (Details) € in Millions	1 Months Ended							12 Months Ended
	Dec. 31, 2019EUR (€)EquityInstruments	Nov. 30, 2019EquityInstruments	Jun. 30, 2019EquityInstruments	Dec. 31, 2018EUR (€)EquityInstruments	Jun. 30, 2018EquityInstruments	Dec. 31, 2017EquityInstruments	Jun. 30, 2017EquityInstruments	Dec. 31, 2019EUR (€)EquityInstruments	Dec. 31, 2018EUR (€)EquityInstruments	Dec. 31, 2017EquityInstruments
Disclosure of contingent liabilities [line items]
Number of options granted | EquityInstruments	921,885	19,800	423,487	861,575	178,900	653,825	120,536	1,365,172	1,040,475	774,361
Minimum
Disclosure of contingent liabilities [line items]
Estimated exposure of stock option	€ 7.6			€ 7.6				€ 7.6	€ 7.6
Maximum
Disclosure of contingent liabilities [line items]
Estimated exposure of stock option	€ 8.6			€ 8.6				€ 8.6	€ 8.6

Commitments (Details)

Commitments (Details) € in Thousands, £ in Millions, $ in Millions	1 Months Ended		12 Months Ended
	Feb. 28, 2019USD ($)	Dec. 31, 2018GBP (£)	Dec. 31, 2019USD ($)	Dec. 31, 2019EUR (€)
Commitments [Line Items]
Commitments to acquire property, plant and equipment | €				€ 0
Commitments to acquire additional intangible assets | €				0
Halozyme | Global Collaboration and License Agreement
Commitments [Line Items]
Payment for each future target | $	$ 10
Future milestone payments | $	160
Payment for additional milestones | $	$ 40
Development milestone payment | $			$ 10
Phase 1 milestone payment | $			$ 5
Lonza Sales AG | Efgartigimod
Commitments [Line Items]
Contractual obligations | £		£ 25.3
Contractual period		5 years
Outstanding commitment | €				53,400
Lonza Sales AG | Cusatuzumab
Commitments [Line Items]
Contractual obligations | €				34,400
Lonza Sales AG | ARGX-117
Commitments [Line Items]
Contractual obligations | €				€ 3,600

Audit Fees (Details)

Audit Fees (Details) - EUR (€) € in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Audit fees
Audit fees(1)	€ 730	€ 648	€ 179
Audit-related fees	159	143	724
Total	€ 889	€ 791	€ 903

Overview of consolidation sco_3

Overview of consolidation scope (Details)	12 Months Ended
	Dec. 31, 2019subsidiary
Netherlands
Overview of consolidation scope
Participation ( as a percent)	100.00%
ARGENX BVBA | Belgium
Overview of consolidation scope
Number of subsidiaries	1
Participation ( as a percent)	100.00%
ARGENX US INC | United States
Overview of consolidation scope
Number of subsidiaries	2
Participation ( as a percent)	100.00%
ARGENX JAPAN KK | Japan
Overview of consolidation scope
Participation ( as a percent)	100.00%