Subsequent events - Additional Information (Detail) - $ / shares	1 Months Ended
Apr. 15, 2017	Mar. 09, 2017
Subsequent Event [Line Items]
Dividends payable, record date	Mar. 31, 2017
Subsequent Event
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share		$ 0.02

The per share amount of a dividend declared, but not paid, as of the financial reporting date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

Name:	us-gaap_DividendsPayableAmountPerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant