Derivatives (Derivatives Not Designated as Hedging Instruments - Interest Rate Contracts) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Derivative assets - Fair value	$ 99,103	$ 66,146
Derivative liabilities - Fair value	133,702	74,935
Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	13,254,731	10,153,108
Derivative assets - Fair value	99,042	66,146
Derivative liabilities - Fair value	126,006	68,136
Derivatives not designated as hedging instruments \| Customer Counterparties
Derivative [Line Items]
Derivative assets - Fair value	12,915
Derivative liabilities - Fair value	132
Derivatives not designated as hedging instruments \| Customer Counterparties \| Written Options
Derivative [Line Items]
Notional amount	907,651	691,548
Derivative assets - Fair value	0	0
Derivative liabilities - Fair value	782	223
Derivatives not designated as hedging instruments \| Customer Counterparties \| Sold Collars and Corridors
Derivative [Line Items]
Notional amount	379,257	247,542
Derivative assets - Fair value	169	204
Derivative liabilities - Fair value	1,343	267
Derivatives not designated as hedging instruments \| Customer Counterparties \| Swaps
Derivative [Line Items]
Notional amount	4,574,216	3,724,295
Derivative assets - Fair value	8,520	32,241
Derivative liabilities - Fair value	97,897	24,879
Derivatives not designated as hedging instruments \| Customer Counterparties \| Total interest rate contracts
Derivative [Line Items]
Notional amount	5,861,124	4,663,385
Derivative assets - Fair value	8,689	32,445
Derivative liabilities - Fair value	100,022	25,369
Derivatives not designated as hedging instruments \| Financial Counterparties
Derivative [Line Items]
Derivative assets - Fair value	65
Derivative liabilities - Fair value	7,780
Derivatives not designated as hedging instruments \| Financial Counterparties \| Purchased Options
Derivative [Line Items]
Notional amount	907,651	691,548
Derivative assets - Fair value	795	233
Derivative liabilities - Fair value	0	0
Derivatives not designated as hedging instruments \| Financial Counterparties \| Collars and Corridors
Derivative [Line Items]
Notional amount	379,257	247,542
Derivative assets - Fair value	1,354	271
Derivative liabilities - Fair value	172	211
Derivatives not designated as hedging instruments \| Financial Counterparties \| Swaps
Derivative [Line Items]
Notional amount	4,581,302	3,731,385
Derivative assets - Fair value	61,780	25,684
Derivative liabilities - Fair value	6,768	32,378
Derivatives not designated as hedging instruments \| Financial Counterparties \| Total interest rate contracts
Derivative [Line Items]
Notional amount	5,868,210	4,670,475
Derivative assets - Fair value	63,929	26,188
Derivative liabilities - Fair value	$ 6,940	$ 32,589

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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