Derivative Instruments And Hedging Activities - Derivative Instruments Not Designated As Hedging Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Liability derivative instruments not designated as hedging instruments	$ 6,308	$ 10,731
Accrued Liabilities [Member] | Foreign Exchange Contracts [Member]
Derivative [Line Items]
Liability derivative instruments not designated as hedging instruments	3,133	3,923
Other Non-Current Liabilities [Member] | Foreign Exchange Contracts [Member]
Derivative [Line Items]
Liability derivative instruments not designated as hedging instruments	$ 3,175	$ 6,808