Related party transactions - Narrative (Details)	6 Months Ended
Jun. 30, 2018 EUR (€) EquityInstruments
Related party transactions
Exercise term of warrants	8 years
Exercise price of warrants \| €	€ 79.88
Number of shares subscribed if warrant is exercised \| EquityInstruments	1
Vesting period of warrants	36 months

The weighted average exercise price of other equity instruments (ie other than share options) granted in a share-based payment arrangement. [Refer: Weighted average [member]]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 2
-IssueDate 2017-01-01
-Paragraph 45
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2017-03-01&anchor=para_45&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_WeightedAverageExercisePriceOfOtherEquityInstrumentsGrantedInSharebasedPaymentArrangement
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration