Commitments and contingencies - Legal proceedings (Detail)	1 Months Ended
May 05, 2017 USD ($) item
Motor Oil MDL \| Pending litigation
Legal proceedings
Number of nationwide classes \| item	2
California County Environmental Authorities \| Minimum
Legal proceedings
Settlement amount \| $	$ 100,000

The amount of loss pertaining to the specified contingency that was charged against earnings in the period, including the effects of revisions in previously reported estimates.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Name:	us-gaap_LossContingencyLossInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration