Shareholders equity - Share options (Details) - EUR (€)	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Shareholders equity
Compensation expenses	€ 2,870,000	€ 2,288,000
Compensation expenses recorded in general and administrative costs	1,121,000	878,000
Compensation expenses recorded in research and development costs	€ 1,749,000	€ 1,410,000

The amount of expense arising from share-based payment transactions in which the goods or services received did not qualify for recognition as assets.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2018-01-01
-Paragraph 51
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2018-03-01&anchor=para_51_a&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_ExpenseFromSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration