Financial Instruments - Additional Information (Details) - Foreign exchange forward contracts - USD ($) $ in Thousands |
12 Months Ended | |
|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Derivative [Line Items] | ||
| Foreign exchange forward contracts, notional value | $ 182,464 | $ 104,344 |
| Remaining maturity, or less (in months) | 12 months | |
| Cash Flow Hedging | ||
| Derivative [Line Items] | ||
| Realized gains and losses related to the maturity of foreign exchange forward contracts | $ 3,398 | $ (475) |
| Cash Flow Hedging | Other Current Assets | ||
| Derivative [Line Items] | ||
| Unrealized losses related to the effective portion of changes in the fair value of foreign exchange forward contracts | 4,230 | |
| Cash Flow Hedging | Other Current Liabilities | ||
| Derivative [Line Items] | ||
| Unrealized losses related to the effective portion of changes in the fair value of foreign exchange forward contracts | $ (795) | |