Derivative Financial Instruments - Impact of Derivatives on Consolidated Statements of Income (Details) - Interest rate swaps - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Trading
Gain (loss) on derivatives, net	$ 1,573	$ 5,649	$ 10,702	$ 5,672
Designated as Hedging Instrument | Fair Value Hedges
Fair Value Hedges
Hedge ineffectiveness gains (losses) recorded in earnings	(1,843)	1,238	(929)	1,488
Realized gains recorded in interest expense	7,531	3,835	22,512	14,081
Trading
Gain (loss) on derivatives, net	5,688	5,073	21,583	15,569
Designated as Hedging Instrument | Cash Flow Hedges
Cash Flow Hedges
Hedge ineffectiveness gains (losses) recorded in earnings	(273)	(303)	(542)	(303)
Realized losses recorded in interest expense	(5,411)	(3,587)	(16,157)	(3,587)
Trading
Gain (loss) on derivatives, net	(5,684)	(3,890)	(16,699)	(3,890)
Trading
Trading
Interest reclassification	853	(1,170)	2,846	(3,137)
Change in fair value of future interest payments recorded in earnings	716	5,636	2,972	(2,870)
Gain (loss) on derivatives, net	$ 1,569	$ 4,466	$ 5,818	$ (6,007)