Available for Sale Securities (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)		Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 8,397,679	$ 8,442,828		$ 8,369,075
Available-for-sale Securities, Fair Value		8,249,432	8,437,291		8,321,578
Available-for-sale Securities, Gross Unrealized Gain		28,760	62,340		41,519
Available-for-sale Securities, Gross Unrealized Loss		(177,007)	(67,813)		(88,625)
Available-for-Sale Securities, Other Than Temporary Impairments		0	(64)		(391)
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		8,397,679	8,442,828		8,369,075
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 8,249,432	8,437,291		8,321,578
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield		2.01%
Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]
Available-for-sale Securities, Proceeds		$ 44,790	240,010
Available-for-sale Securities, Gross realized gains		193	2,092
Available-for-sale Securities, Gross realized losses		(483)	(43)
Available-for-sale Securities, Related federal and state income tax expense		74	797
Available-for-sale Securities, Pledged as Collateral [Abstract]
Available-for-sale Securities, Pledged As Collateral, Amortized cost		8,289,623	6,647,659		7,151,468
Available-for-sale Securities, Pledged As Collateral, Fair value		$ 8,124,367	$ 6,629,319		$ 7,089,346
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		502	445		534
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 4,758,537	$ 4,557,042		$ 3,773,942
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,937,405	214,460		2,118,360
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		6,695,942	4,771,502		5,892,302
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		96,756	62,863		30,648
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		80,251	5,014		58,368
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		177,007	67,877		89,016
Fixed Maturity Securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis		23,894
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		1,023,948
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		1,502,536
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		283,672
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		2,834,051
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value		23,816
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		1,008,607
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		1,469,488
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		277,440
Available-for-sale Securities, Debt Maturities, Single Maturity Date		$ 2,779,351
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		1.96%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.94%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield		2.06%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield		2.07%
Available-for-sale Securities, Debt Maturities, Nominal Yield		2.02%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	7.06
U.S. Treasury
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 493	1,000		1,000
Available-for-sale Securities, Fair Value		491	999		1,000
Available-for-sale Securities, Gross Unrealized Gain		0	0		0
Available-for-sale Securities, Gross Unrealized Loss		(2)	(1)		0
Available-for-Sale Securities, Other Than Temporary Impairments		0	0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis		0
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		493
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		0
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		493
Available-for-sale Securities, Debt Maturities, Amortized Cost		493	1,000		1,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value		0
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		491
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Single Maturity Date		491
Available-for-sale Securities, Debt Maturities, Fair Value		$ 491	$ 999		$ 1,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.99%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.99%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	1.84
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		1	1		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 491	$ 999		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		491	999		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		2	1		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		2	1		0
Municipal and other tax-exempt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		20,428	35,555		27,182
Available-for-sale Securities, Fair Value		20,414	35,453		27,080
Available-for-sale Securities, Gross Unrealized Gain		136	343		181
Available-for-sale Securities, Gross Unrealized Loss		(150)	(445)		(283)
Available-for-Sale Securities, Other Than Temporary Impairments		0	0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis		5,687
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		2,282
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		12,459
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		20,428
Available-for-sale Securities, Debt Maturities, Amortized Cost		20,428	35,555		27,182
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value		5,692
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		2,391
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		12,331
Available-for-sale Securities, Debt Maturities, Single Maturity Date		20,414
Available-for-sale Securities, Debt Maturities, Fair Value		$ 20,414	$ 35,453		$ 27,080
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield	[2]	3.18%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield	[2]	6.27%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield	[2]	0.00%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield	[2],[3]	2.84%
Available-for-sale Securities, Debt Maturities, Nominal Yield	[2]	3.32%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	10.02
Available-for-sale Securities, Debt Maturities, Effective tax rate for nominal yield calculation		25.00%
Available-for-sale Securities, Debt Maturities, Number of days for interest rates to reset		35 days
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		13	12		19
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 12,935	$ 1,407		$ 12,765
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,891	4,623		4,802
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		14,826	6,030		17,567
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		8	1		18
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		142	444		265
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		150	445		283
Commercial mortgage-backed securities guaranteed by U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		2,787,630	2,895,258		2,858,885
Available-for-sale Securities, Fair Value		2,732,966	2,877,028		2,834,961
Available-for-sale Securities, Gross Unrealized Gain		1,998	4,883		1,963
Available-for-sale Securities, Gross Unrealized Loss		(56,662)	(23,113)		(25,887)
Available-for-Sale Securities, Other Than Temporary Impairments		0	0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis		18,207
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		1,021,173
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		1,502,536
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		245,714
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		2,787,630
Available-for-sale Securities, Debt Maturities, Amortized Cost		2,787,630	2,895,258		2,858,885
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value		18,124
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		1,005,725
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		1,469,488
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		239,629
Available-for-sale Securities, Debt Maturities, Single Maturity Date		2,732,966
Available-for-sale Securities, Debt Maturities, Fair Value		$ 2,732,966	$ 2,877,028		$ 2,834,961
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		1.58%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.93%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield		2.06%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield		2.08%
Available-for-sale Securities, Debt Maturities, Nominal Yield		2.01%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	6.97
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		216	161		185
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 1,658,562	$ 1,828,685		$ 1,465,703
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		582,971	36,305		652,296
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,241,533	1,864,990		2,117,999
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		36,141	22,758		11,824
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		20,521	355		14,063
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		56,662	23,113		25,887
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		25,500	4,400		25,500
Available-for-sale Securities, Fair Value		25,480	4,153		25,481
Available-for-sale Securities, Gross Unrealized Gain		48	0		50
Available-for-sale Securities, Gross Unrealized Loss		(68)	(247)		(69)
Available-for-Sale Securities, Other Than Temporary Impairments		0	0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost Basis		0
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		0
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		25,500
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		25,500
Available-for-sale Securities, Debt Maturities, Amortized Cost		25,500	4,400		25,500
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value		0
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		25,480
Available-for-sale Securities, Debt Maturities, Single Maturity Date		25,480
Available-for-sale Securities, Debt Maturities, Fair Value		$ 25,480	$ 4,153		$ 25,481
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield	[3]	1.59%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.59%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	14.43
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		2	2		2
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 19,961	$ 0		$ 19,959
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		472	4,153		472
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		20,433	4,153		20,431
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		40	0		41
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		28	247		28
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		68	247		69
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		5,563,628	5,473,555		5,429,459
Available-for-sale Securities, Fair Value		5,470,081	5,481,542		5,402,373
Available-for-sale Securities, Gross Unrealized Gain		26,578	51,971		35,605
Available-for-sale Securities, Gross Unrealized Loss		(120,125)	(43,920)		(62,300)
Available-for-Sale Securities, Other Than Temporary Impairments		0	(64)		(391)
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis		5,563,628
Available-for-sale Securities, Debt Maturities, Amortized Cost		5,563,628	5,473,555		5,429,459
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value		5,470,081
Available-for-sale Securities, Debt Maturities, Fair Value		$ 5,470,081	$ 5,481,542		$ 5,402,373
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield	[4]	2.00%
Available-for-sale Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities		4 years 110 days
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		270	165		217
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 3,066,588	$ 2,723,835		$ 2,274,604
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,352,071	168,523		1,458,587
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		4,418,659	2,892,358		3,733,191
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		60,565	40,063		18,758
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		59,560	3,921		43,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		120,125	43,984		62,691
U.S. government agency residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		5,493,194	5,380,183		5,355,148
Available-for-sale Securities, Fair Value		5,379,921	5,372,916		5,309,152
Available-for-sale Securities, Gross Unrealized Gain		6,852	36,639		16,304
Available-for-sale Securities, Gross Unrealized Loss		(120,125)	(43,906)		(62,300)
Available-for-Sale Securities, Other Than Temporary Impairments		0	0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		5,493,194	5,380,183		5,355,148
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 5,379,921	$ 5,372,916		$ 5,309,152
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		270	159		209
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 3,066,588	$ 2,717,030		$ 2,268,706
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,352,071	155,062		1,458,587
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		4,418,659	2,872,092		3,727,293
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		60,565	40,026		18,367
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		59,560	3,880		43,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		120,125	43,906		62,300
U.S. government agency residential mortgage-backed securities | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		3,107,874	3,126,933		3,021,551
Available-for-sale Securities, Fair Value		3,041,408	3,126,083		2,997,563
Available-for-sale Securities, Gross Unrealized Gain		4,197	26,304		11,549
Available-for-sale Securities, Gross Unrealized Loss		(70,663)	(27,154)		(35,537)
Available-for-Sale Securities, Other Than Temporary Impairments		0	0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		3,107,874	3,126,933		3,021,551
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 3,041,408	$ 3,126,083		$ 2,997,563
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		156	83		113
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 1,815,606	$ 1,595,879		$ 1,203,041
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		755,589	68,215		824,029
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,571,195	1,664,094		2,027,070
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		35,077	25,623		9,618
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		35,586	1,531		25,919
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		70,663	27,154		35,537
U.S. government agency residential mortgage-backed securities | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		1,567,520	1,401,752		1,545,971
Available-for-sale Securities, Fair Value		1,532,582	1,399,011		1,531,009
Available-for-sale Securities, Gross Unrealized Gain		1,390	7,836		3,148
Available-for-sale Securities, Gross Unrealized Loss		(36,328)	(10,577)		(18,110)
Available-for-Sale Securities, Other Than Temporary Impairments		0	0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		1,567,520	1,401,752		1,545,971
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 1,532,582	$ 1,399,011		$ 1,531,009
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		82	51		69
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 998,792	$ 795,586		$ 863,778
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		361,326	17,284		385,816
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,360,118	812,870		1,249,594
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		21,502	10,001		7,297
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		14,826	576		10,813
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		36,328	10,577		18,110
U.S. government agency residential mortgage-backed securities | Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		817,800	851,498		787,626
Available-for-sale Securities, Fair Value		805,931	847,822		780,580
Available-for-sale Securities, Gross Unrealized Gain		1,265	2,499		1,607
Available-for-sale Securities, Gross Unrealized Loss		(13,134)	(6,175)		(8,653)
Available-for-Sale Securities, Other Than Temporary Impairments		0	0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		817,800	851,498		787,626
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 805,931	$ 847,822		$ 780,580
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		32	25		27
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 252,190	$ 325,565		$ 201,887
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		235,156	69,563		248,742
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		487,346	395,128		450,629
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		3,986	4,402		1,452
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		9,148	1,773		7,201
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		13,134	6,175		8,653
Privately issued residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		70,434	93,372		74,311
Available-for-sale Securities, Fair Value		90,160	108,626		93,221
Available-for-sale Securities, Gross Unrealized Gain		19,726	15,332		19,301
Available-for-sale Securities, Gross Unrealized Loss		0	(14)		0
Available-for-Sale Securities, Other Than Temporary Impairments		0	(64)		(391)
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		70,434	93,372		74,311
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 90,160	$ 108,626		$ 93,221
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		0	6	[5]	8	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 0	$ 6,805	[5]	$ 5,898	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0	13,461	[5]	0	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		0	20,266	[5]	5,898	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0	37	[5]	391	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0	41	[5]	0	[6]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ 0	78	[5]	391	[6]
Perpetual preferred stock
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost			15,562		12,562
Available-for-sale Securities, Fair Value			19,272		15,767
Available-for-sale Securities, Gross Unrealized Gain			3,710		3,205
Available-for-sale Securities, Gross Unrealized Loss			0		0
Available-for-Sale Securities, Other Than Temporary Impairments			0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost			15,562		12,562
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value			$ 19,272		$ 15,767
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions			0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value			$ 0		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value			0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value			0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss			0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss			0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss			0		0
Equity securities and mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost			17,498		14,487
Available-for-sale Securities, Fair Value			18,844		14,916
Available-for-sale Securities, Gross Unrealized Gain			1,433		515
Available-for-sale Securities, Gross Unrealized Loss			(87)		(86)
Available-for-Sale Securities, Other Than Temporary Impairments			0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost			17,498		14,487
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value			$ 18,844		$ 14,916
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions			104		111
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value			$ 2,116		$ 911
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value			856		2,203
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value			2,972		3,114
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss			40		7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss			47		79
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss			$ 87		$ 86

[1] Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.

[2] Calculated on a taxable equivalent basis using a 25 percent effective tax rate.

[3] Nominal yield on municipal and other tax-exempt securities and other debt securities with contractual maturity dates over ten years are based on variable rates which generally are reset within 35 days.

[4] The nominal yield on mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary –– Unaudited following for current yields on available for sale securities portfolio.

[5] Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.

[6] Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.