Research and development costs (Details) - EUR (€)	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Research and development costs
Research and development costs	€ 8,587,000	€ 9,523,000	€ 21,412,000	€ 21,487,000

The amount of expenditure directly attributable to research or development activities, recognised in profit or loss.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 38
-IssueDate 2018-01-01
-Paragraph 126
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=38&date=2018-03-01&anchor=para_126&doctype=Standard
-URIDate 2018-03-16

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