Accumulated other comprehensive loss - Components of Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			$ (382)
Unrealized gain on derivative instruments, net of tax	$ 271	$ (31)	936	$ 72
Foreign currency translation adjustment	1,559	$ 198	(3,301)	$ 574
Ending Balance	(2,747)		(2,747)
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(482)
Foreign currency translation adjustment			(3,301)
Ending Balance	(3,783)		(3,783)
Change in Fair Value [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			100
Unrealized gain on derivative instruments, net of tax			936
Ending Balance	1,036		1,036
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance			(382)
Unrealized gain on derivative instruments, net of tax			936
Foreign currency translation adjustment			(3,301)
Ending Balance	$ (2,747)		$ (2,747)