Commitments and Contingencies - Effect of Financial Derivatives on Statements of Income (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
Foreign Exchange Contracts [Member] | Derivatives not Designated as Hedging Instruments [Member] | Other Expense (Income) [Member] | |||
Derivative Instruments, Gain (Loss) [Line Items] | |||
Amount of Gain or (Loss) Recognized in Income on Derivatives | $ (1,847) | $ 1,566 | $ 366 |