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
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain Recognized in OCI	$ 5,818	$ (5,319)
Amount of Gain Reclassified from Accumulated OCI to Statement of Operations	$ 759	$ (4,431)