Derivative Financial Instruments - Impact of Derivatives on Consolidated Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest rate swaps:
Total	$ 953	$ (547)	$ 1,602	$ 3,292	$ 825	$ 5,401	$ (9,458)	$ (764)	$ 13,765	$ 7,892	$ 29,308
Interest Rate Swaps | Fair Value
Interest rate swaps:
Hedge ineffectiveness gains (losses) recorded in earnings									2,695	1,718	(558)
Realized gains recorded in interest expense									29,940	20,958	28,668
Total									32,635	22,676	28,110
Interest Rate Swaps | Cash Flow
Interest rate swaps:
Total									(22,902)	(9,590)	0
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net									(1,427)	(520)	0
Gain (Loss) from Components Excluded from Assessment of Cash Flow Hedge Effectiveness, Net									(21,475)	(9,070)	0
Interest Rate Swaps | Trading
Interest rate swaps:
Interest reclassification									3,451	(2,250)	1,285
Change in fair value of future interest payments recorded in earnings									581	(2,944)	(87)
Total									$ 4,032	$ (5,194)	$ 1,198