Hedging - Cash Flow Hedging Instruments (Details) - Unrealized Holding Gains (Losses), Net of Tax, On Foreign Currency Forward Contracts - Reclassification out of Accumulated Other Comprehensive Income - Foreign currency forward contracts - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Revenues	$ 6,839	$ (6,485)
Not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Other Income	$ 3,151	$ 1,539