Derivative instruments - Schedule of Gain (Loss) Recognized on Derivative Instruments (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments [Line Items]
Cross-currency swap gain (loss) recorded in other comprehensive income (loss), net of taxes	$ 263	$ (437)	$ (90)
Interest Rate Swap [Member]
Derivative Instruments [Line Items]
Interest rate swap gain recognized in net income (loss)			1,254
Cross-currency swap [Member]
Derivative Instruments [Line Items]
Cross-currency swap gain (loss) recorded in other comprehensive income (loss), net of taxes	$ 263	$ (437)	$ (90)