Fair Value Measurements (Investment and Derivative Information) (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Fair Value Measurements | |||
| Assets related to derivative instruments | $ 0 | $ 0 | |
| Liabilities related to derivative instruments | 0 | 0 | |
| Foreign exchange contracts | Other income expense, net | Not designated as hedging instrument | |||
| Fair Value Measurements | |||
| Foreign exchange forward contracts | $ (1,662) | $ 418 | $ 200 |
| Minimum | |||
| Fair Value Measurements | |||
| Maturity period of long-term investments | 1 year | ||
| Maximum | |||
| Fair Value Measurements | |||
| Maturity period of long-term investments | 2 years | ||