Summary of significant accounting policies – Leases (Details)	Aug. 04, 2018 property
Summary of significant accounting policies
Number of expected lease locations	1,200

The number of units (items of property) under operating lease arrangements.

No definition available.

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant