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
		Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Weighted average of U.S. dollar equivalent of foreign denominated net assets		$ 1,094,210	$ 1,677,145
Derivative gains (losses)	[1]	$ (2,323)	$ 29,398

[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.