Derivatives - Gain (Loss) in the Consolidated Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Not designated as hedging instrument | Foreign currency forward contracts | Other expense
Derivative [Line Items]
Gain (loss) on derivative	$ 1,143	$ (1,459)	$ 3,181	$ (4,150)