Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 6,837,571invest_DerivativeNotionalAmount	$ 6,691,851invest_DerivativeNotionalAmount
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	4,177	19,718
Financial derivatives, at fair value	84,844	75,708
Derivative, Collateral [Abstract]
Collateral Pledged	46,627	11,320
Derivative Asset	4,177us-gaap_DerivativeAssets	19,718us-gaap_DerivativeAssets
Derivative Liability	38,217us-gaap_DerivativeLiabilities	64,388us-gaap_DerivativeLiabilities
Cash [Member]
Derivative, Collateral [Abstract]
Obligation to Return Securities Received as Collateral	0	0
Collateral Pledged	46,600	9,800
Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	1,000,000	900,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	0
Financial derivatives, at fair value	31,718	28,989
Derivative, Weighted-Average Pay Rate	2.47%	2.25%
Derivative, Weighted-Average Receive Rate	0.23%	0.24%
Derivative, Average Remaining Maturity	3 years 11 months 23 days	3 years 3 months 0 days
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	15,000	10,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	68
Financial derivatives, at fair value	289	0
Derivative, Weighted-Average Pay Rate	2.43%	2.50%
Derivative, Weighted-Average Receive Rate	0.51%	0.48%
Derivative, Average Remaining Maturity	6 years 2 months 23 days	6 years 11 months 12 days
Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Derivative Credit Risk Valuation Adjustment, Derivative Assets	22	201
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	187	156
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	490,183	806,596
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	537	7,570
Financial derivatives, at fair value	51,224	45,360
Derivative, Weighted-Average Pay Rate	4.23%	4.63%
Derivative, Weighted-Average Receive Rate	0.23%	0.24%
Derivative, Average Remaining Maturity	7 years 0 months 18 days	4 years 10 months 10 days
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap, Receive Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	3,829,355	4,324,663
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	3,414	11,836
Financial derivatives, at fair value	461	262
Derivative, Weighted-Average Pay Rate	0.14%	0.27%
Derivative, Weighted-Average Receive Rate	0.27%	0.70%
Derivative, Average Remaining Maturity	0 years 6 months 18 days	0 years 6 months 11 days
Not Designated as Hedging Instrument [Member] \| Interest Rate Swap, Receive Fixed Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	383,565	175,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	1	83
Financial derivatives, at fair value	877	934
Derivative, Weighted-Average Pay Rate	0.12%	0.10%
Derivative, Weighted-Average Receive Rate	1.34%	0.65%
Derivative, Average Remaining Maturity	3 years 5 months 19 days	3 years 3 months 18 days
Not Designated as Hedging Instrument [Member] \| Basis Swap [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	1,105,000	404,288
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	247	276
Financial derivatives, at fair value	406	318
Derivative, Weighted-Average Pay Rate	0.11%	0.32%
Derivative, Weighted-Average Receive Rate	0.31%	0.29%
Derivative, Average Remaining Maturity	2 years 5 months 1 day	1 year 6 months 7 days
Not Designated as Hedging Instrument [Member] \| Forward Contracts [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	12,768	65,704
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	86
Financial derivatives, at fair value	53	0
Derivative, Weighted-Average Forward Price	$ 101.00	$ 98.91
Not Designated as Hedging Instrument [Member] \| Future [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	1,700	5,600
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	0
Financial derivatives, at fair value	$ 3	$ 1
Derivative, Weighted-Average Forward Price	$ 126.60	$ 123.02

Derivative, Weighted-Average Forward Price

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- Definition

Derivative, Weighted-Average Pay Rate

+ References

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- Definition

Derivative, Weighted-Average Receive Rate

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- Definition

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

+ References

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

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4H

-Subparagraph (d)

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Fair value, after the 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 not elected to be offset.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

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-Topic 210

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- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Amount of credit risk valuation adjustment to derivative assets to properly reflect the credit quality of the counterparties.

+ References

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- Definition

Amount of credit risk valuation adjustment to derivative liabilities to properly reflect the credit quality of the entity.

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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 elected not to be offset. Excludes assets not subject to a master netting arrangement.

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-Topic 210

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-Paragraph 3

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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 elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value, after the 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 not elected to be offset.

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- Definition

The fair value of collateral received by the entity associated with securities borrowed that must be returned if the counterparty fulfills its obligations. It appears on the balance sheet as a liability and has a corresponding asset that appears on the balance sheet called Securities Received as Collateral.

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-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.15)

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-Glossary Collateral

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