Derivatives - Gain (Loss) in the Consolidated Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Not designated as hedging instrument | Foreign currency forward contracts | Other expense
Derivative [Line Items]
Gain (loss) on derivative	$ 3,153	$ (1,834)	$ 2,038	$ (2,692)