Derivative Financial Instruments Derivative Instruments and Hedging Activities - Cash Flow Hedge Activity Included in Accumulated Other Comprehensive Income (Loss) (Details) - Cost of Sales [Member] - Foreign Exchange Forward [Member] - Cash Flow Hedging [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	$ 1,743	$ (318)	$ (2,256)	$ (2,144)
Derivative Instruments, Gain Recognized in Other Comprehensive Income (Loss), Effective Portion	(1,743)	318	2,256	2,144
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion	$ 192	$ 534	$ 687	$ 556