General and administrative costs (Details) - EUR (€)	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
General and administrative costs
General and administrative expense	€ 2,903,000	€ 2,579,000	€ 8,970,000	€ 7,900,000

The amount of expense relating to general and administrative activities of the entity.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2018-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_112_c&doctype=Standard
-URIDate 2018-03-16

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