Derivative Instruments - Derivative instruments designated as hedges of the net investment in a foreign operation - Summary (Details) - Derivatives designated as hedging instruments - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Weighted average of U.S. dollar equivalent of foreign denominated net assets		$ 1,119,999	$ 1,659,312	$ 1,107,105	$ 1,668,229
Derivative gains (losses)	[1]	$ 48,099	$ (49,370)	$ 45,776	$ (78,767)

[1] Derivative gains (losses) from derivative instruments designated as hedges of the net investment in a foreign operation are recorded in the cumulative translation adjustment account within AOCI for each period.