Derivative Instruments And Hedging Activities - Derivative Instruments Not Designated As Hedging Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Liability derivative instruments not designated as hedging instruments	$ 4,018	$ 6,308
Accrued Liabilities | Foreign Exchange Contracts
Derivative [Line Items]
Liability derivative instruments not designated as hedging instruments	2,925	3,133
Other Liabilities | Foreign Exchange Contracts
Derivative [Line Items]
Liability derivative instruments not designated as hedging instruments	$ 1,093	$ 3,175