Operating costs - Summary of sales and marketing expenses (Details) - EUR (€) € in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Expenses by nature [abstract]
Personnel costs	€ (2,156)	€ (1,167)	€ (785)
Other operating expenses	(646)	(618)	(397)
Total sales and marketing expenses	€ (2,803)	€ (1,785)	€ (1,182)

The amount of expense relating to the marketing and selling of goods or services.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
-Paragraph 85
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_85&doctype=Standard
-URIDate 2017-03-09

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