Derivative Financial Instruments - Impact of Derivatives on Consolidated Statements of Income (Details) - Interest rate swaps - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Trading
Gain (loss) on derivatives, net	$ 1,816	$ (4,170)
Designated as Hedging Instrument \| Fair Value Hedges
Fair Value Hedges
Hedge ineffectiveness gains (losses) recorded in earnings	5,853	(4,167)
Realized gains (losses) recorded in interest expense	(514)	4,547
Trading
Gain (loss) on derivatives, net	5,339	380
Designated as Hedging Instrument \| Cash Flow Hedges
Cash Flow Hedges
Hedge ineffectiveness losses recorded in earnings	2,684	(72)
Realized losses recorded in interest expense	(1,562)	(3,339)
Trading
Gain (loss) on derivatives, net	1,122	(3,411)
Trading
Trading
Interest reclassification	110	80
Realized losses recorded in earnings	(4,755)	(1,219)
Gain (loss) on derivatives, net	$ (4,645)	$ (1,139)

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=84234895&loc=SL5618551-113959

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-Publisher FASB
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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
-SubTopic 10
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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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-Section 50
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The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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