The total number of new claims filed pertaining to a loss contingency during the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

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

Commitments and contingencies - Additional information (Details)		1 Months Ended	12 Months Ended
	Aug. 01, 2016 employee	Aug. 31, 2016 lawsuit	Feb. 03, 2018 employee
EPA Collective Action
Loss Contingencies [Line Items]
Number of employees opted in lawsuit \| employee	10,314		9,124
S.D.N.Y. Cases
Loss Contingencies [Line Items]
New claims filed, number \| lawsuit		2