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, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivatives designated as hedging instruments
Derivative [Line Items]
Weighted average of U.S. dollar equivalent of foreign denominated net assets	$ 2,687,455	$ 2,523,821
Derivative gains (losses)	$ 960	$ 60,614