Derivative Financial Instruments - Balance Sheet Location And Fair Value Of Assets And Liabilities Associated With Derivative Financial Instruments (Detail) - Foreign exchange contracts - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments	$ 314	$ 258
Other Current Assets
Derivatives, Fair Value [Line Items]
Derivatives not designated as hedging instruments	$ 840	$ 566