Cash and cash equivalents (Details) - EUR (€) € in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and cash equivalents
Cash	€ 238,208	€ 52,729
Short-term deposits	66,693	117,292
Total cash and cash equivalents	304,901	170,021	€ 100,635	€ 29,728
Restricted cash in cash and cash equivalents	€ 0	€ 0

The amount of cash on hand and demand deposits. [Refer: Cash on hand]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

The amount of cash on hand and demand deposits, along with short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value. [Refer: Cash; Cash equivalents]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-IssueDate 2020-01-01
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-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2020-en-r&anchor=para_45&doctype=Standard
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- References

No definition available.

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- Definition

A classification of cash equivalents representing short-term deposits. [Refer: Cash equivalents]

+ References

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- Definition

Amount of cash restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=121583591&loc=SL98516268-108586

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-SubTopic 210
-Section S99
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