Marketable Securities - Summary of Marketable Securities (Detail) - EUR (€) € in Thousands	Jun. 30, 2021	Dec. 31, 2020
Disclosure Detailed Information About Marketable Securities [Line Items]
Non-current financial assets available-for-sale	€ 90,693	€ 115,280
Current financial assets available-for-sale	166,094	134,278
Financial assets at amortised cost, class [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	256,787	249,558
Non-current financial assets available-for-sale	90,693	115,280
Current financial assets available-for-sale	166,094	134,278
Financial assets	256,787	249,558
Financial assets at amortised cost, class [member] \| Prime [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	6,398	7,716
Financial assets at amortised cost, class [member] \| High grade [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	127,690	142,339
Financial assets at amortised cost, class [member] \| Upper Medium Grade [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	119,785	99,503
Financial assets at amortised cost, class [member] \| Lower Medium Grade [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	2,914
Financial assets at amortised cost, class [member] \| Fixed interest rate [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	231,342	175,757
Financial assets at amortised cost, class [member] \| Floating interest rate [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	16,613	16,975
Financial assets at amortised cost, class [member] \| Zero Coupon [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	8,832	56,826
Financial assets at amortised cost, class [member] \| US Treasury bills [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	0	46,243
Financial assets at amortised cost, class [member] \| US Government bonds [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	85,049	62,088
Financial assets at amortised cost, class [member] \| Commercial papers [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	8,832	10,583
Financial assets at amortised cost, class [member] \| Corporate bonds [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	144,830	121,282
Financial assets at amortised cost, class [member] \| Agency bonds [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	18,076	9,362
Financial assets at fair value, class [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	256,693	249,530
Non-current financial assets available-for-sale	90,623	115,277
Current financial assets available-for-sale	166,070	134,253
Financial assets	256,693	249,530
Financial assets at fair value, class [member] \| Prime [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	6,398	7,714
Financial assets at fair value, class [member] \| High grade [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	127,678	142,352
Financial assets at fair value, class [member] \| Upper Medium Grade [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	119,706	99,464
Financial assets at fair value, class [member] \| Lower Medium Grade [member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	2,911
Financial assets at fair value, class [member] \| Fixed interest rate [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	231,249	175,732
Financial assets at fair value, class [member] \| Floating interest rate [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	16,611	16,972
Financial assets at fair value, class [member] \| Zero Coupon [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets	8,833	56,826
Financial assets at fair value, class [member] \| US Treasury bills [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	0	46,245
Financial assets at fair value, class [member] \| US Government bonds [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	85,049	62,101
Financial assets at fair value, class [member] \| Commercial papers [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	8,833	10,581
Financial assets at fair value, class [member] \| Corporate bonds [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	144,734	121,234
Financial assets at fair value, class [member] \| Agency bonds [Member]
Disclosure Detailed Information About Marketable Securities [Line Items]
Financial assets available-for-sale	€ 18,077	€ 9,369

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The amount of current financial assets available-for-sale. [Refer: Financial assets available-for-sale; Current financial assets]

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The amount of assets that are: (a) cash; (b) an equity instrument of another entity; (c) a contractual right: (i) to receive cash or another financial asset from another entity; or (ii) to exchange financial assets or financial liabilities with another entity under conditions that are potentially favourable to the entity; or (d) a contract that will, or may be, settled in the entity’s own equity instruments and is: (i) a non-derivative for which the entity is, or may be, obliged to receive a variable number of the entity’s own equity instruments; or (ii) a derivative that will, or may be, settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the entity’s own equity instruments. For this purpose the entity’s own equity instruments do not include puttable financial instruments classified as equity instruments in accordance with paragraphs 16A-16B of IAS 32, instruments that impose on the entity an obligation to deliver to another party a pro rata share of the net assets of the entity only on liquidation and are classified as equity instruments in accordance with paragraphs 16C-16D of IAS 32, or instruments that are contracts for the future receipt or delivery of the entity’s own equity instruments. [Refer: Financial instruments, class [member]; Financial liabilities]

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The amount of non-derivative financial assets that are designated as available for sale or are not classified as (a) loans and receivables; (b) held-to-maturity investments; or (c) financial assets at fair value through profit or loss. [Refer: Derivative financial assets; Financial assets at fair value through profit or loss; Held-to-maturity investments]

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The amount of non-current financial assets available-for-sale. [Refer: Financial assets available-for-sale; Non-current financial assets]

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