Derivative Financial Instruments - Impact of Derivatives on Consolidated Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Trading
Total	$ (4,114)	$ 1,368	$ 2,142	$ (354)	$ 953	$ (547)	$ 1,602	$ 3,292
Interest Rate Swaps
Trading
Total									$ 9,188	$ 13,765	$ 7,892
Interest Rate Swaps | Designated as Hedging Instrument | Fair Value
Fair Value Hedges
Hedge ineffectiveness (losses) gains recorded in earnings(1)									(1,035)	2,695	1,718
Realized gains recorded in interest expense									27,810	29,940	20,958
Trading
Total									26,775	32,635	22,676
Interest Rate Swaps | Designated as Hedging Instrument | Cash Flow
Cash Flow Hedges
Hedge ineffectiveness losses recorded in earnings(1)									(1,579)	(1,427)	(520)
Realized losses recorded in interest expense									(17,665)	(21,475)	(9,070)
Trading
Total									(19,244)	(22,902)	(9,590)
Interest Rate Swaps | Trading
Trading
Interest reclassification									2,170	3,451	(2,250)
Change in fair value of future interest payments recorded in earnings									(513)	581	(2,944)
Total									$ 1,657	$ 4,032	$ (5,194)