Accumulated other comprehensive income - Components of Changes in Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 2,699
Unrealized gain on cross-currency swap, net of tax of $25	103	(318)
Foreign currency translation adjustment	439	(2,708)
Ending Balance	3,241
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	2,846
Unrealized gain on cross-currency swap, net of tax of $25
Foreign currency translation adjustment	439
Ending Balance	3,285
Fair Value of Cross-Currency Swap [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(147)
Unrealized gain on cross-currency swap, net of tax of $25	103
Foreign currency translation adjustment
Ending Balance	(44)
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	2,699
Unrealized gain on cross-currency swap, net of tax of $25	103
Foreign currency translation adjustment	439
Ending Balance	$ 3,241