Derivatives and Hedge Accounting - Summary of Effect of Foreign Currency Exchange Contracts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
(Gain)/loss recognized in consolidated statements of income	$ (2,839)	$ (5,597)	$ (2,744)
Derivatives in cash flow hedging relationships | Derivative designated as hedging instruments | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
(Gain)/loss recognized in AOCI	$ (19,802)	$ (5,129)