Derivative Financial Instruments - Impact of Derivatives on Consolidated Statements of Income (Details) - Interest rate swaps - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Trading
Gain (loss) on derivatives, net	$ 3,700	$ (4,885)	$ 9,130	$ 24
Designated as Hedging Instrument | Fair Value Hedges
Fair Value Hedges
Hedge ineffectiveness gains (losses) recorded in earnings	489	(8,049)	915	(8,172)
Realized gains recorded in interest expense	7,490	4,573	14,982	10,246
Trading
Gain (loss) on derivatives, net	7,979	(3,476)	15,897	2,074
Designated as Hedging Instrument | Cash Flow Hedges
Cash Flow Hedges
Hedge ineffectiveness gains (losses) recorded in earnings	34	0	(270)	0
Realized losses recorded in interest expense	(5,392)	0	(10,746)	0
Trading
Gain (loss) on derivatives, net	(5,358)	0	(11,016)	0
Trading
Trading
Interest reclassification	970	(2,427)	1,993	(1,967)
Change in fair value of future interest payments recorded in earnings	109	1,018	2,256	(83)
Gain (loss) on derivatives, net	$ 1,079	$ (1,409)	$ 4,249	$ (2,050)