Available for Sale Securities (Details) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2018 USD ($)		Jun. 30, 2017 USD ($)		Jun. 30, 2018 USD ($)		Jun. 30, 2017 USD ($)		Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 8,343,468		$ 8,325,000		$ 8,343,468		$ 8,325,000		$ 8,369,075
Available-for-sale Securities, Fair Value		8,162,866		8,341,041		8,162,866		8,341,041		8,321,578
Available-for-sale Securities, Gross Unrealized Gain		24,586		65,740		24,586		65,740		41,519
Available-for-sale Securities, Gross Unrealized Loss		(204,815)		(49,699)		(204,815)		(49,699)		(88,625)
Available-for-Sale Securities, Other Than Temporary Impairments		(373)		0		(373)		0		(391)
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		8,343,468		8,325,000		8,343,468		8,325,000		8,369,075
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 8,162,866		8,341,041		$ 8,162,866		8,341,041		8,321,578
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield		2.14%				2.14%
Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]
Available-for-sale Securities, Proceeds		$ 142,743		460,402		$ 187,533		700,412
Available-for-sale Securities, Gross realized gains		257		2,763		450		4,855
Available-for-sale Securities, Gross realized losses		(1,019)		(2,383)		(1,502)		(2,426)
Available-for-sale Securities, Related federal and state income tax expense		(194)		148		(268)		945
Available-for-sale Securities, Pledged as Collateral [Abstract]
Available-for-sale Securities, Pledged As Collateral, Amortized cost		6,821,287		6,327,666		6,821,287		6,327,666		7,151,468
Available-for-sale Securities, Pledged As Collateral, Fair value		$ 6,653,875		$ 6,317,623		$ 6,653,875		$ 6,317,623		$ 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		532		367		532		367		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		$ 5,127,395		$ 3,818,331		$ 5,127,395		$ 3,818,331		$ 3,773,942
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,846,965		268,886		1,846,965		268,886		2,118,360
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		6,974,360		4,087,217		6,974,360		4,087,217		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		120,246		44,025		120,246		44,025		30,648
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		84,942		5,674		84,942		5,674		58,368
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		205,188		49,699		205,188		49,699		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		12,644				12,644
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		990,041				990,041
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		1,548,520				1,548,520
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		285,332				285,332
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		2,836,537				2,836,537
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Fair Value		12,621				12,621
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		971,431				971,431
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		1,512,106				1,512,106
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		278,924				278,924
Available-for-sale Securities, Debt Maturities, Single Maturity Date		$ 2,775,082				$ 2,775,082
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		2.31%				2.31%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.97%				1.97%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield		2.17%				2.17%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield		2.17%				2.17%
Available-for-sale Securities, Debt Maturities, Nominal Yield		2.10%				2.10%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	6.95				6.95
U.S. Treasury
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 494		1,000		$ 494		1,000		1,000
Available-for-sale Securities, Fair Value		490		998		490		998		1,000
Available-for-sale Securities, Gross Unrealized Gain		0		0		0		0		0
Available-for-sale Securities, Gross Unrealized Loss		(4)		(2)		(4)		(2)		0
Available-for-Sale Securities, Other Than Temporary Impairments		0		0		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				0
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		494				494
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		0				0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		0				0
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		494				494
Available-for-sale Securities, Debt Maturities, Amortized Cost		494		1,000		494		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				0
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		490				490
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0				0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		0				0
Available-for-sale Securities, Debt Maturities, Single Maturity Date		490				490
Available-for-sale Securities, Debt Maturities, Fair Value		$ 490		$ 998		$ 490		$ 998		$ 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%				0.00%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.99%				1.99%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield		0.00%				0.00%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield		0.00%				0.00%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.99%				1.99%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	1.59				1.59
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		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		$ 490		$ 997		$ 490		$ 997		$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0		0		0		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		490		997		490		997		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		4		2		4		2		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0		0		0		0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		4		2		4		2		0
Municipal and other tax-exempt securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		10,590		32,885		10,590		32,885		27,182
Available-for-sale Securities, Fair Value		10,697		32,765		10,697		32,765		27,080
Available-for-sale Securities, Gross Unrealized Gain		111		293		111		293		181
Available-for-sale Securities, Gross Unrealized Loss		(4)		(413)		(4)		(413)		(283)
Available-for-Sale Securities, Other Than Temporary Impairments		0		0		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		4,574				4,574
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		2,303				2,303
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		0				0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		3,713				3,713
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		10,590				10,590
Available-for-sale Securities, Debt Maturities, Amortized Cost		10,590		32,885		10,590		32,885		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		4,580				4,580
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		2,401				2,401
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0				0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		3,716				3,716
Available-for-sale Securities, Debt Maturities, Single Maturity Date		10,697				10,697
Available-for-sale Securities, Debt Maturities, Fair Value		$ 10,697		$ 32,765		$ 10,697		$ 32,765		$ 27,080
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield	[2]	3.45%				3.45%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield	[2]	6.27%				6.27%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield	[2]	0.00%				0.00%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield	[2],[3]	3.98%				3.98%
Available-for-sale Securities, Debt Maturities, Nominal Yield	[2]	4.25%				4.25%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	6.53				6.53
Available-for-sale Securities, Debt Maturities, Effective tax rate for nominal yield calculation		25.00%				25.00%
Available-for-sale Securities, Debt Maturities, Number of days for interest rates to reset		35
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		10		13		10		13		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		$ 4,784		$ 1,957		$ 4,784		$ 1,957		$ 12,765
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		495		4,655		495		4,655		4,802
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		5,279		6,612		5,279		6,612		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		3		1		3		1		18
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		1		412		1		412		265
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		4		413		4		413		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		2,799,953		2,788,543		2,799,953		2,788,543		2,858,885
Available-for-sale Securities, Fair Value		2,738,451		2,782,070		2,738,451		2,782,070		2,834,961
Available-for-sale Securities, Gross Unrealized Gain		1,815		7,804		1,815		7,804		1,963
Available-for-sale Securities, Gross Unrealized Loss		(63,317)		(14,277)		(63,317)		(14,277)		(25,887)
Available-for-Sale Securities, Other Than Temporary Impairments		0		0		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		8,070				8,070
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		987,244				987,244
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		1,548,520				1,548,520
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		256,119				256,119
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		2,799,953				2,799,953
Available-for-sale Securities, Debt Maturities, Amortized Cost		2,799,953		2,788,543		2,799,953		2,788,543		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		8,041				8,041
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		968,540				968,540
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		1,512,106				1,512,106
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		249,764				249,764
Available-for-sale Securities, Debt Maturities, Single Maturity Date		2,738,451				2,738,451
Available-for-sale Securities, Debt Maturities, Fair Value		$ 2,738,451		$ 2,782,070		$ 2,738,451		$ 2,782,070		$ 2,834,961
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		1.67%				1.67%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.96%				1.96%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield		2.17%				2.17%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield		2.20%				2.20%
Available-for-sale Securities, Debt Maturities, Nominal Yield		2.10%				2.10%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	6.89				6.89
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		211		121		211		121		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		$ 1,675,839		$ 1,388,406		$ 1,675,839		$ 1,388,406		$ 1,465,703
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		554,819		78,828		554,819		78,828		652,296
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,230,658		1,467,234		2,230,658		1,467,234		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		42,732		12,690		42,732		12,690		11,824
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		20,585		1,587		20,585		1,587		14,063
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		63,317		14,277		63,317		14,277		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		4,400		25,500
Available-for-sale Securities, Fair Value		25,444		4,152		25,444		4,152		25,481
Available-for-sale Securities, Gross Unrealized Gain		12		0		12		0		50
Available-for-sale Securities, Gross Unrealized Loss		(68)		(248)		(68)		(248)		(69)
Available-for-Sale Securities, Other Than Temporary Impairments		0		0		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				0
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost Basis		0				0
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Amortized Cost Basis		0				0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost Basis		25,500				25,500
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		25,500				25,500
Available-for-sale Securities, Debt Maturities, Amortized Cost		25,500		4,400		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				0
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		0				0
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		0				0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		25,444				25,444
Available-for-sale Securities, Debt Maturities, Single Maturity Date		25,444				25,444
Available-for-sale Securities, Debt Maturities, Fair Value		$ 25,444		$ 4,152		$ 25,444		$ 4,152		$ 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%				0.00%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		0.00%				0.00%
Available-for-sale Securities, Debt Maturities, Six To Ten Years, Nominal Yield		0.00%				0.00%
Available-for-sale Securities, Debt Maturities, Over Ten Years, Nominal Yield	[3]	1.59%				1.59%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.59%				1.59%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[1]	14.18				14.18
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		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		$ 0		$ 0		$ 0		$ 0		$ 19,959
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		20,434		4,152		20,434		4,152		472
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		20,434		4,152		20,434		4,152		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		0		0		0		0		41
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		68		248		68		248		28
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		68		248		68		248		69
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		5,506,931		5,468,038		5,506,931		5,468,038		5,429,459
Available-for-sale Securities, Fair Value		5,387,784		5,485,760		5,387,784		5,485,760		5,402,373
Available-for-sale Securities, Gross Unrealized Gain		22,648		52,418		22,648		52,418		35,605
Available-for-sale Securities, Gross Unrealized Loss		(141,422)		(34,696)		(141,422)		(34,696)		(62,300)
Available-for-Sale Securities, Other Than Temporary Impairments		(373)		0		(373)		0		(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		5,506,931				5,506,931
Available-for-sale Securities, Debt Maturities, Amortized Cost		5,506,931		5,468,038		5,506,931		5,468,038		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		5,387,784				5,387,784
Available-for-sale Securities, Debt Maturities, Fair Value		$ 5,387,784		$ 5,485,760		$ 5,387,784		$ 5,485,760		$ 5,402,373
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield	[4]	2.16%				2.16%
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		308		139		308		139		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		$ 3,446,282		$ 2,425,303		$ 3,446,282		$ 2,425,303		$ 2,274,604
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,271,217		180,364		1,271,217		180,364		1,458,587
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		4,717,499		2,605,667		4,717,499		2,605,667		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		77,507		31,310		77,507		31,310		18,758
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		64,288		3,386		64,288		3,386		43,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		141,795		34,696		141,795		34,696		62,691
U.S. government agency residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		5,441,555		5,381,382		5,441,555		5,381,382		5,355,148
Available-for-sale Securities, Fair Value		5,304,560		5,382,377		5,304,560		5,382,377		5,309,152
Available-for-sale Securities, Gross Unrealized Gain		4,427		35,691		4,427		35,691		16,304
Available-for-sale Securities, Gross Unrealized Loss		(141,422)		(34,696)		(141,422)		(34,696)		(62,300)
Available-for-Sale Securities, Other Than Temporary Impairments		0		0		0		0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		5,441,555		5,381,382		5,441,555		5,381,382		5,355,148
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 5,304,560		$ 5,382,377		$ 5,304,560		$ 5,382,377		$ 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		300		139		300		139		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		$ 3,440,873		$ 2,425,303		$ 3,440,873		$ 2,425,303		$ 2,268,706
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,271,217		180,364		1,271,217		180,364		1,458,587
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		4,712,090		2,605,667		4,712,090		2,605,667		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		77,134		31,310		77,134		31,310		18,367
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		64,288		3,386		64,288		3,386		43,933
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		141,422		34,696		141,422		34,696		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		3,088,585		3,005,920		3,088,585		3,005,920		3,021,551
Available-for-sale Securities, Fair Value		3,007,885		3,008,531		3,007,885		3,008,531		2,997,563
Available-for-sale Securities, Gross Unrealized Gain		2,774		24,213		2,774		24,213		11,549
Available-for-sale Securities, Gross Unrealized Loss		(83,474)		(21,602)		(83,474)		(21,602)		(35,537)
Available-for-Sale Securities, Other Than Temporary Impairments		0		0		0		0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		3,088,585		3,005,920		3,088,585		3,005,920		3,021,551
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 3,007,885		$ 3,008,531		$ 3,007,885		$ 3,008,531		$ 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		174		75		174		75		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		$ 2,049,432		$ 1,381,687		$ 2,049,432		$ 1,381,687		$ 1,203,041
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		710,962		87,371		710,962		87,371		824,029
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,760,394		1,469,058		2,760,394		1,469,058		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		44,860		20,288		44,860		20,288		9,618
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		38,614		1,314		38,614		1,314		25,919
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		83,474		21,602		83,474		21,602		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		1,580,185		1,412,376		1,580,185		1,412,376		1,545,971
Available-for-sale Securities, Fair Value		1,538,582		1,412,472		1,538,582		1,412,472		1,531,009
Available-for-sale Securities, Gross Unrealized Gain		738		7,785		738		7,785		3,148
Available-for-sale Securities, Gross Unrealized Loss		(42,341)		(7,689)		(42,341)		(7,689)		(18,110)
Available-for-Sale Securities, Other Than Temporary Impairments		0		0		0		0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		1,580,185		1,412,376		1,580,185		1,412,376		1,545,971
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 1,538,582		$ 1,412,472		$ 1,538,582		$ 1,412,472		$ 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		93		42		93		42		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		$ 1,116,337		$ 731,853		$ 1,116,337		$ 731,853		$ 863,778
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		339,515		16,388		339,515		16,388		385,816
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,455,852		748,241		1,455,852		748,241		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		26,663		7,213		26,663		7,213		7,297
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		15,678		476		15,678		476		10,813
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		42,341		7,689		42,341		7,689		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		772,785		938,086		772,785		938,086		787,626
Available-for-sale Securities, Fair Value		758,093		936,365		758,093		936,365		780,580
Available-for-sale Securities, Gross Unrealized Gain		915		3,641		915		3,641		1,607
Available-for-sale Securities, Gross Unrealized Loss		(15,607)		(5,362)		(15,607)		(5,362)		(8,653)
Available-for-Sale Securities, Other Than Temporary Impairments		0		0		0		0		0
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		772,785		938,086		772,785		938,086		787,626
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 758,093		$ 936,365		$ 758,093		$ 936,365		$ 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		33		21		33		21		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		$ 275,104		$ 291,806		$ 275,104		$ 291,806		$ 201,887
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		220,740		76,605		220,740		76,605		248,742
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		495,844		368,411		495,844		368,411		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		5,611		3,766		5,611		3,766		1,452
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		9,996		1,596		9,996		1,596		7,201
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		15,607		5,362		15,607		5,362		8,653
U.S. government agency residential mortgage-backed securities | Other
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost				25,000				25,000
Available-for-sale Securities, Fair Value				25,009				25,009
Available-for-sale Securities, Gross Unrealized Gain				52				52
Available-for-sale Securities, Gross Unrealized Loss				(43)				(43)
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				25,000				25,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value				$ 25,009				$ 25,009
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions				1				1
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				$ 19,957				$ 19,957
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				19,957				19,957
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				43				43
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				43				43
Privately issued residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		65,376		86,656		65,376		86,656		74,311
Available-for-sale Securities, Fair Value		83,224		103,383		83,224		103,383		93,221
Available-for-sale Securities, Gross Unrealized Gain		18,221		16,727		18,221		16,727		19,301
Available-for-sale Securities, Gross Unrealized Loss		0		0		0		0		0
Available-for-Sale Securities, Other Than Temporary Impairments		(373)		0		(373)		0		(391)
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Amortized Cost		65,376		86,656		65,376		86,656		74,311
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value		$ 83,224		$ 103,383		$ 83,224		$ 103,383		$ 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		8	[5]	0	[6]	8	[5]	0	[6]	8	[7]
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		$ 5,409	[5]	$ 0	[6]	$ 5,409	[5]	$ 0	[6]	$ 5,898	[7]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0	[5]	0	[6]	0	[5]	0	[6]	0	[7]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		5,409	[5]	0	[6]	5,409	[5]	0	[6]	5,898	[7]
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		373	[5]	0	[6]	373	[5]	0	[6]	391	[7]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0	[5]	0	[6]	0	[5]	0	[6]	0	[7]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ 373	[5]	0	[6]	$ 373	[5]	0	[6]	391	[7]
Perpetual preferred stock
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost				12,562				12,562		12,562
Available-for-sale Securities, Fair Value				16,568				16,568		15,767
Available-for-sale Securities, Gross Unrealized Gain				4,006				4,006		3,205
Available-for-sale Securities, Gross Unrealized Loss				0				0		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, Amortized Cost				12,562				12,562		12,562
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value				$ 16,568				$ 16,568		$ 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		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		$ 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				0				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		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				0				0		0
Equity securities and mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost				17,572				17,572		14,487
Available-for-sale Securities, Fair Value				18,728				18,728		14,916
Available-for-sale Securities, Gross Unrealized Gain				1,219				1,219		515
Available-for-sale Securities, Gross Unrealized Loss				(63)				(63)		(86)
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				17,572				17,572		14,487
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Fair Value				$ 18,728				$ 18,728		$ 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				91				91		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				$ 1,668				$ 1,668		$ 911
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value				887				887		2,203
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value				2,555				2,555		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				22				22		7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss				41				41		79
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss				$ 63				$ 63		$ 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.

[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.

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