Hedging - Notional Amount (Details) - Foreign currency forward contracts - Designated as hedging instruments - Cash flow hedging - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional amount of foreign currency forward contract	$ 639,016	$ 505,218
Euro
Derivative [Line Items]
Notional amount of foreign currency forward contract	448,778	335,179
British pound sterling
Derivative [Line Items]
Notional amount of foreign currency forward contract	65,278	73,460
Australian dollar
Derivative [Line Items]
Notional amount of foreign currency forward contract	77,010	52,820
Canadian dollar
Derivative [Line Items]
Notional amount of foreign currency forward contract	$ 47,950	$ 43,759