Summary of significant accounting policies (details)	Jan. 01, 2017 USD ($)
ASU 2016-09
Recently Adopted Accounting Standards Updates
Net cumulative effect on retained earnings	$ 0

Amount of the cumulative effect on retained earnings net of related income tax effect.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration