Fair Value Measurements and Derivative Instruments (Derivative Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Total net derivative (liability) asset	$ (1,381)	$ 1,563
Total derivative assets
Derivative [Line Items]
Total net derivative (liability) asset	2,507	1,898
Total derivative liabilities
Derivative [Line Items]
Total net derivative (liability) asset	(3,888)	(335)
Foreign exchange contracts | Derivatives designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative (liability) asset	80	57
Foreign exchange contracts | Derivatives designated as hedging instruments | Accounts payable and accrued liabilities
Derivative [Line Items]
Total net derivative (liability) asset	(60)	(144)
Foreign exchange contracts | Derivatives not designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative (liability) asset	2,427	65
Foreign exchange contracts | Derivatives not designated as hedging instruments | Accounts payable and accrued liabilities
Derivative [Line Items]
Total net derivative (liability) asset	(3,828)	(191)
Interest rate swap | Derivatives designated as hedging instruments | Other current assets and prepayments
Derivative [Line Items]
Total net derivative (liability) asset	$ 0	$ 1,776