Significant accounting policies - Impairment of tangible and intangible assets (Details)	12 Months Ended
Dec. 31, 2017 EUR (€)
Significant accounting policies
Impairment loss recognized	€ 0

The amount of impairment loss recognised in profit or loss. [Refer: Impairment loss; Profit (loss)]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2017-01-01
-Paragraph 126
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_126_a&doctype=Standard
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 36
-IssueDate 2017-01-01
-Paragraph 129
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2017-03-01&anchor=para_129_a&doctype=Standard
-URIDate 2017-03-09

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration