Income taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Tax Credit Carryforward [Line Items]
Net deferred tax liabilities	$ 3,996
Net deferred income tax asset		$ 3,593
Net increase (decrease) in valuation allowance	200	(300)
Deferred tax assets relating to NOL carryforwards	6,275	6,428
Anticipated refunds received from previously-filed carryback claims			$ 2,800
Domestic Tax Authority
Tax Credit Carryforward [Line Items]
Net deferred tax liabilities	1,200
Net deferred income tax asset		3,800
Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Net deferred tax liabilities	2,800	$ 300
Foreign tax credits carry forwards, deferred tax asset valuation allowances released			$ 5,000
Tax credit carry forwards	$ 6,200