Segment information - Narratives (Details)	6 Months Ended
Jun. 30, 2017 restaurant segment
Segment Reporting [Abstract]
Number of reportable segments \| segment	6
Number of restaurants \| restaurant	1

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration