Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 8,429,964	$ 6,837,571
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	3,816	4,177
Financial derivatives, at fair value	77,199	84,844
Derivative Credit Risk Valuation Adjustment, Derivative Assets	200	200
Derivative, Collateral [Abstract]
Collateral Pledged	37,986	46,627
Derivative Asset	3,816	4,177
Derivative Liability	39,213	38,217
Cash [Member]
Derivative, Collateral [Abstract]
Obligation to Return Securities Received as Collateral	0	0
Collateral Pledged	38,000	46,600
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	1,276,285	1,000,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	949	0
Financial derivatives, at fair value	$ 26,703	$ 31,718
Derivative, Average Fixed Interest Rate	2.35%	2.47%
Derivative, Average Variable Interest Rate	0.37%	0.23%
Derivative, Average Remaining Maturity	4 years 1 month 28 days	3 years 11 months 23 days
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 119,000	$ 15,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	8	0
Financial derivatives, at fair value	$ 1,381	$ 289
Derivative, Average Fixed Interest Rate	2.25%	2.43%
Derivative, Average Variable Interest Rate	0.64%	0.51%
Derivative, Average Remaining Maturity	7 years 11 days	6 years 2 months 23 days
Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 5	$ 22
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	170	187
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	454,041	490,183
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	229	537
Financial derivatives, at fair value	$ 44,528	$ 51,224
Derivative, Average Fixed Interest Rate	3.73%	4.23%
Derivative, Average Variable Interest Rate	0.33%	0.23%
Derivative, Average Remaining Maturity	6 years 7 days	7 years 18 days
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Receive Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 5,590,638	$ 3,829,355
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	2,384	3,414
Financial derivatives, at fair value	$ 4,205	$ 461
Derivative, Average Fixed Interest Rate	0.47%	0.27%
Derivative, Average Variable Interest Rate	0.31%	0.14%
Derivative, Average Remaining Maturity	6 months 25 days	6 months 18 days
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Receive Fixed Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 230,000	$ 383,565
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	1
Financial derivatives, at fair value	$ 421	$ 877
Derivative, Average Fixed Interest Rate	0.91%	1.34%
Derivative, Average Variable Interest Rate	0.41%	0.12%
Derivative, Average Remaining Maturity	2 years 3 months 4 days	3 years 5 months 19 days
Not Designated as Hedging Instrument [Member] | Basis Swap [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 725,000	$ 1,105,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	232	247
Financial derivatives, at fair value	$ 131	$ 406
Derivative, Average Variable Interest Rate	0.22%	0.11%
Derivative, Variable Interest Rate	0.38%	0.31%
Derivative, Average Remaining Maturity	2 years 3 months 29 days	2 years 5 months 1 day
Not Designated as Hedging Instrument [Member] | Forward Contracts [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 0	$ 12,768
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0	0
Financial derivatives, at fair value	$ 0	$ 53
Derivative, Weighted-Average Forward Price	$ 0.00	$ 101.00
Not Designated as Hedging Instrument [Member] | Future [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 35,000	$ 1,700
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	19	0
Financial derivatives, at fair value	$ 0	$ 3
Derivative, Weighted-Average Forward Price	$ 125.96	$ 126.60