Derivative Instruments - Schedule of derivative instruments designated as hedges of the net investment in a foreign operation (Details) (Designated as Hedging Instrument, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Designated as Hedging Instrument
Derivative [Line Items]
Weighted average of U.S. dollar equivalent of foreign denominated net assets	$ 2,384,508		$ 2,648,137
Derivative gains (losses)	$ 120,643	[1]	$ (27,392)	[1]

[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.