Derivative Instruments - Designated as Hedging Instruments by Classification and Amount of Gains and Losses (Details) - Derivatives designated as hedging instruments - Foreign currency forward exchange contracts - Cost of sales - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain Recognized in OCI	$ 3,215	$ (24,009)	$ 15,548	$ (63,999)
Amount of (Loss) Reclassified from Accumulated OCI to Statement of Operations	$ (787)	$ (9,241)	$ (10,004)	$ (6,648)