Income taxes - Loss Carryforwards (Details) € in Thousands	Dec. 31, 2019 EUR (€)
Corporation tax
Carryforward
Gross loss carryforwards	€ 37,988
Trade tax losses
Carryforward
Gross loss carryforwards	37,222
Foreign loss carryforwards
Carryforward
Gross loss carryforwards	€ 17,357

The amount of unused tax losses for which no deferred tax asset is recognised in the statement of financial position. [Refer: Unused tax losses [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 12
-IssueDate 2019-01-01
-Paragraph 81
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_e&doctype=Standard
-URIDate 2019-03-27

Name:	ifrs-full_UnusedTaxLossesForWhichNoDeferredTaxAssetRecognised
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant