Fair Value Measurements and Derivative Instruments (Derivative Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Total net derivative asset	$ 48	$ 1,296
Total derivative assets
Derivative [Line Items]
Total net derivative asset	345	2,031
Total derivative liabilities
Derivative [Line Items]
Total net derivative asset	(297)	(735)
Foreign exchange contracts | Derivatives designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative asset	51	61
Foreign exchange contracts | Derivatives designated as hedging instruments | Accounts payable and accrued liabilities
Derivative [Line Items]
Total net derivative asset	(190)	(104)
Foreign exchange contracts | Derivatives not designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative asset	294	1,970
Foreign exchange contracts | Derivatives not designated as hedging instruments | Accounts payable and accrued liabilities
Derivative [Line Items]
Total net derivative asset	$ (107)	$ (631)