Change in Fair Values of Derivative Not Designated as Hedging Instruments Recorded in Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Foreign currency contracts | (Gain)/loss on foreign currency | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Loss on foreign currency	$ 25,339	$ 5,909	$ 7,597