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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Trading
Gain (loss) on derivatives, net	$ 4,947	$ 3,700	$ 7,231	$ 9,130
Designated as Hedging Instrument \| Fair Value Hedges
Fair Value Hedges
Hedge ineffectiveness gains (losses) recorded in earnings	1,218	489	(1,199)	915
Realized gains recorded in interest expense	7,391	7,490	14,650	14,982
Trading
Gain (loss) on derivatives, net	8,609	7,979	13,451	15,897
Designated as Hedging Instrument \| Cash Flow Hedges
Cash Flow Hedges
Hedge ineffectiveness (losses) gains recorded in earnings	(403)	34	(681)	(270)
Realized losses recorded in interest expense	(4,586)	(5,392)	(9,207)	(10,746)
Trading
Gain (loss) on derivatives, net	(4,989)	(5,358)	(9,888)	(11,016)
Trading
Trading
Interest reclassification	672	970	1,360	1,993
Change in fair value of future interest payments recorded in earnings	655	109	2,308	2,256
Gain (loss) on derivatives, net	$ 1,327	$ 1,079	$ 3,668	$ 4,249

Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net, Hedge Ineffectiveness

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Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net, Interest Reclassification

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5618551-113959

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The net gain (loss) relating to components of the gain (loss) on the cash flow hedging instrument excluded from the assessment of cash flow hedge effectiveness. Recognized in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of gain (loss)recognized in the income statement from the hedging ineffectiveness of a fair value hedge.

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