Fair Value Measurements and Derivative Instruments (Derivative Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Total net derivative asset	$ 3,319	$ 1,563
Total derivative assets
Derivative [Line Items]
Total net derivative asset	3,497	1,898
Total derivative liabilities
Derivative [Line Items]
Total net derivative asset	(178)	(335)
Foreign exchange contracts | Derivatives designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative asset	114	57
Foreign exchange contracts | Derivatives designated as hedging instruments | Accounts payable and accrued liabilities
Derivative [Line Items]
Total net derivative asset	(39)	(144)
Foreign exchange contracts | Derivatives not designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative asset	2,559	65
Foreign exchange contracts | Derivatives not designated as hedging instruments | Accounts payable and accrued liabilities
Derivative [Line Items]
Total net derivative asset	(139)	(191)
Interest rate swap | Derivatives designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative asset	$ 824	$ 1,776