Financial Derivatives - Schedule of Derivative Instruments in Statement of Financial Position (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 8,493,388		$ 8,100,257
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	2,674		23,182
Financial derivatives, at fair value	(32,054)		(58,152)
Derivative, Collateral [Abstract]
Collateral Pledged	25,075		25,643
Derivative Asset	2,674		23,182
Derivative Liability	6,979		32,509
Cash [Member]
Derivative, Collateral [Abstract]
Obligation to Return Securities Received as Collateral	0		0
Collateral Pledged	100		1,000
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	1,808,581		1,642,609
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	1,292		18,508
Financial derivatives, at fair value	$ (9,133)		$ (18,909)
Derivative, Average Fixed Interest Rate	1.77%		1.73%
Derivative, Average Variable Interest Rate	1.04%		0.90%
Derivative, Average Remaining Maturity	4 years 9 months	4 years 8 months 13 days
Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Interest Rate Swap, Receive Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 860,200
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	11
Financial derivatives, at fair value	$ (1,815)
Derivative, Average Fixed Interest Rate	0.98%
Derivative, Average Variable Interest Rate	1.39%
Derivative, Average Remaining Maturity	3 years 3 months 7 days
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 221,000		$ 207,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	843		3,706
Financial derivatives, at fair value	$ (290)		$ (955)
Derivative, Average Fixed Interest Rate	2.28%		2.18%
Derivative, Average Variable Interest Rate	1.34%		1.11%
Derivative, Average Remaining Maturity	7 years 1 month 18 days	7 years 3 months 10 days
Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Derivative Credit Risk Valuation Adjustment, Derivative Assets	$ 0		$ 14
Derivative Credit Risk Valuation Adjustment, Derivative Liabilities	121		158
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Pay Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	433,406		435,827
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	400		339
Financial derivatives, at fair value	$ (20,912)		$ (32,951)
Derivative, Average Fixed Interest Rate	4.06%		4.06%
Derivative, Average Variable Interest Rate	1.04%		0.89%
Derivative, Average Remaining Maturity	5 years 8 months 10 days	5 years 10 months 24 days
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Receive Fixed Non-Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 4,262,401		$ 4,991,821
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	69		607
Financial derivatives, at fair value	$ 0		$ (5,064)
Derivative, Average Fixed Interest Rate	0.87%		0.75%
Derivative, Average Variable Interest Rate	0.82%		0.74%
Derivative, Average Remaining Maturity	9 months 15 days	7 months 5 days
Not Designated as Hedging Instrument [Member] | Interest Rate Swap, Receive Fixed Callable [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 30,000		$ 30,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	0		0
Financial derivatives, at fair value	$ (10)		$ (33)
Derivative, Average Fixed Interest Rate	0.58%		0.58%
Derivative, Average Variable Interest Rate	0.97%		0.82%
Derivative, Average Remaining Maturity	30 days	4 months
Not Designated as Hedging Instrument [Member] | Basis Swap [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 865,000		$ 765,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	51		36
Financial derivatives, at fair value	$ (15)		$ (243)
Derivative, Average Variable Interest Rate	0.93%		0.78%
Derivative, Variable Interest Rate	0.99%		0.78%
Derivative, Average Remaining Maturity	11 months 5 days	10 months 15 days
Not Designated as Hedging Instrument [Member] | Future [Member]
Notional Disclosures [Abstract]
Derivative, Notional Amount	$ 12,800		$ 28,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral [Abstract]
Financial derivatives, at fair value	8		0
Financial derivatives, at fair value	$ 0		$ (155)
Derivative, Weighted-Average Forward Price	$ 124.62	$ 123.73