Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 6,671,380	$ 6,691,851
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	5,743	19,718
Financial derivatives, at fair value	69,995	75,708
Derivative, Collateral [Abstract]
Collateral Pledged	29,788	11,320
Derivative Asset	5,743	19,718
Derivative Liability	40,207	64,388
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	23,979	28,989
Derivative, Weighted-Average Pay Rate	2.47%	2.25%
Derivative, Weighted-Average Receive Rate	0.24%	0.24%
Derivative, Average Remaining Maturity	4 years 2 months 23 days	3 years 3 months 0 days
Cash Flow Hedging [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	10,000	10,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	68
Financial derivatives, at fair value	81	0
Derivative, Weighted-Average Pay Rate	2.50%	2.50%
Derivative, Weighted-Average Receive Rate	0.48%	0.48%
Derivative, Average Remaining Maturity	6 years 2 months 12 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	76	201
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	264	156
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	492,496	806,596
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	1,775	7,570
Financial derivatives, at fair value	43,694	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 3 months 7 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	3,818,832	4,324,663
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	3,806	11,836
Financial derivatives, at fair value	564	262
Derivative, Weighted-Average Pay Rate	0.14%	0.27%
Derivative, Weighted-Average Receive Rate	0.24%	0.70%
Derivative, Average Remaining Maturity	0 years 5 months 23 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	296,000	175,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	83
Financial derivatives, at fair value	1,152	934
Derivative, Weighted-Average Pay Rate	0.09%	0.10%
Derivative, Weighted-Average Receive Rate	0.86%	0.65%
Derivative, Average Remaining Maturity	3 years 0 months 18 days	3 years 3 months 18 days
Not Designated as Hedging Instrument [Member] | Basis Swap [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	1,030,000	404,288
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	238	276
Financial derivatives, at fair value	758	318
Derivative, Weighted-Average Pay Rate	0.12%	0.32%
Derivative, Weighted-Average Receive Rate	0.29%	0.29%
Derivative, Average Remaining Maturity	2 years 3 months 7 days	1 year 6 months 7 days
Not Designated as Hedging Instrument [Member] | Forward Contracts [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	17,352	65,704
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	86
Financial derivatives, at fair value	10	0
Derivative, Weighted-Average Forward Price	$ 98.01	$ 98.91
Not Designated as Hedging Instrument [Member] | Future [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	6,700	5,600
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	0
Financial derivatives, at fair value	21	1
Derivative, Weighted-Average Forward Price	$ 124.33	$ 123.02
Cash [Member]
Derivative, Collateral [Abstract]
Obligation to Return Securities Received as Collateral	0	0
Collateral Pledged	$ 29,800	$ 9,800