Derivative Financial Instruments - Notional Values (Details) (Interest rate swaps [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Notional values	$ 4,227,216	$ 2,664,755
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional values	678,967	575,131
Cash Flow Hedges [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional values	1,100,226	0
Fair Value Hedges [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional values	$ 2,448,023	$ 2,089,624