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	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 3,503
Unrealized gain(loss)	103		(318)
Foreign currency translation adjustment	376		(2,679)
Ending Balance	3,982	[1]
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	3,651
Foreign currency translation adjustment	376
Ending Balance	4,027
Change in Fair Value [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance				(148)
Ending Balance	(45)			(148)
Change in Fair Value [Member] | Cross-currency swap and warrants [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gain(loss)	103
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	3,503
Foreign currency translation adjustment	376
Ending Balance	3,982
Accumulated Other Comprehensive Income [Member] | Cross-currency swap and warrants [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized gain(loss)	$ 103

[1] Unaudited