Summary of significant accounting policies - Right-of-use assets (Details) - EUR (€) € in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases
Right-of-use	€ 3,191	€ 3,984
Property
Leases
Right-of-use	2,892	3,658
Machinery
Leases
Right-of-use	45	72
Other PPE
Leases
Right-of-use	€ 254	€ 254

The amount of assets that represent a lessee's right to use an underlying asset for the lease term. Underlying asset is an asset that is the subject of a lease, for which the right to use that asset has been provided by a lessor to a lessee.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 16
-IssueDate 2020-01-01
-Paragraph 53
-Subparagraph j
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2020-en-r&anchor=para_53_j&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_RightofuseAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant