Research and development costs (Details) - EUR (€) € in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Research and development costs
Research and development costs	€ 5,990	€ 7,552	€ 13,675	€ 15,582

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 2017-01-01
-Paragraph 126
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=38&date=2017-03-01&anchor=para_126&doctype=Standard
-URIDate 2017-03-09

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