Fair Value Measurements and Derivative Instruments (Derivative Instruments) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Total net derivative (liability) asset	$ (1,820)	$ 1,296
Total derivative assets
Derivative [Line Items]
Total net derivative (liability) asset	1,610	2,031
Total derivative liabilities
Derivative [Line Items]
Total net derivative (liability) asset	(3,430)	(735)
Foreign exchange contracts | Derivatives designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative (liability) asset	175	61
Foreign exchange contracts | Derivatives designated as hedging instruments | Accounts payable and accrued liabilities
Derivative [Line Items]
Total net derivative (liability) asset	0	(104)
Foreign exchange contracts | Derivatives not designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative (liability) asset	1,435	1,970
Foreign exchange contracts | Derivatives not designated as hedging instruments | Accounts payable and accrued liabilities
Derivative [Line Items]
Total net derivative (liability) asset	$ (3,430)	$ (631)