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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Derivatives designated as hedging instruments
Derivative [Line Items]
Weighted average of U.S. dollar equivalent of foreign denominated net assets	$ 2,270,090	$ 2,588,385	$ 2,478,772	$ 2,556,103
Derivative gains (losses)	$ (2,170)	$ (6,135)	$ (1,210)	$ 54,479