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Derivative instruments - Schedule of Fair Values of Derivative Instruments (Detail) (Other long-term assets [Member], Cross-currency swap [Member], USD $)
In Thousands, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Other long-term assets [Member] | Cross-currency swap [Member]
   
Derivatives, Fair Value [Line Items]    
Fair value: favorable (unfavorable) $ 1,778 $ 1,011