Number of pending claims pertaining to a loss contingency.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Name:	us-gaap_LossContingencyPendingClaimsNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Commitments and contingencies - Additional information (Details)	Jan. 04, 2017 employee	Apr. 23, 2013 lawsuit
Zale Corporation
Loss Contingencies [Line Items]
Pending claims \| lawsuit		3
EPA Collective Action
Loss Contingencies [Line Items]
Number of employees opted in lawsuit \| employee	10,456