Fair Value Measurement - Effect of Derivative Instruments on Consolidated Statements of Income for Derivatives Not Designated as Accounting Hedges (Detail) - Cost of Revenues - Not Designated as Hedging Instrument - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Foreign Exchange Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 457	$ (603)
Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 269	$ 0