Available for Sale Securities (Details)		12 Months Ended
		Dec. 31, 2016 USD ($)		Dec. 31, 2015 USD ($)		Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 8,691,728,000		$ 9,004,624,000
Available-for-sale Securities, Fair Value		8,676,829,000		9,042,733,000
Available-for-sale Securities, Gross Unrealized Gain		60,165,000	[1]	79,970,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(74,846,000)	[1]	(41,034,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ (218,000)	[3]	(827,000)	[4]
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.84%
Available-for-sale Securities, Gross Realized Gain (Loss), Disclosures [Abstract]
Available-for-sale Securities, Proceeds		$ 899,381,000		1,600,380,000		$ 2,664,740,000
Available-for-sale Securities, Gross realized gains		11,696,000		15,849,000		24,923,000
Available-for-sale Securities, Gross realized losses		(21,000)		(3,791,000)		(23,384,000)
Available-for-sale Securites, Related federal and state income tax expense		4,542,000		4,691,000		599,000
Available-for-sale Securities, Pledged as Collateral [Abstract]
Available-for-sale Securities, Pledged As Collateral, Amortized cost		7,353,116,000		6,831,743,000
Available-for-sale Securities, Pledged As Collateral, Fair value		$ 7,327,470,000		$ 6,849,524,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		488		419
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		$ 5,231,605,000		$ 3,873,809,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		178,249,000		716,700,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		5,409,854,000		4,590,509,000
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		70,818,000		28,496,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		4,246,000		13,365,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		75,064,000		41,861,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost		27,747,000
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value		28,568,000
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost		10,391,000
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value		10,414,000
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost		111,957,000
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value		128,832,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost		8,541,633,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value		8,509,015,000
Fixed maturity securities [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		41,758,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		935,235,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		1,834,638,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		270,569,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		3,082,200,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less Than One Year, Fair Value		41,759,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		933,506,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		1,822,778,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		266,034,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 3,064,077,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		1.89%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.82%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield		1.85%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield		1.84%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.83%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[5]	6.95
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		$ 1,000,000		1,000,000
Available-for-sale Securities, Fair Value		999,000		995,000
Available-for-sale Securities, Gross Unrealized Gain		0	[1]	0	[2]
Available-for-sale Securities, Gross Unrealized Loss		(1,000)	[1]	(5,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		0	[3]	$ 0	[4]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		1,000,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		1,000,000
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		999,000
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, Fair value		$ 999,000
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		0.87%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Nominal Yield		0.87%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[5]	1.04
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		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		$ 999,000		$ 995,000
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		999,000		995,000
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		1,000		5,000
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		1,000		5,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost		1,000,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value		999,000
Municipal and other tax-exempt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		41,050,000		56,681,000
Available-for-sale Securities, Fair Value		40,993,000		56,817,000
Available-for-sale Securities, Gross Unrealized Gain		343,000	[1]	873,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(400,000)	[1]	(737,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		0	[3]	$ 0	[4]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		9,848,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		12,254,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		2,103,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		16,845,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		41,050,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less Than One Year, Fair Value		9,903,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		12,399,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		2,151,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		16,540,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 40,993,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield	[6]	4.81%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield	[6]	4.01%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield	[6]	3.47%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield	[6],[7]	2.28%
Available-for-sale Securities, Debt Maturities, Nominal Yield	[6]	3.46%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[5]	7.95
Available-for-sale Securities, Debt Maturities, Effective tax rate for nominal yield calculation		39.00%
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 Securities		24		20
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		$ 15,666,000		$ 9,909,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		4,689,000		11,664,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		20,355,000		21,573,000
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		22,000		27,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		378,000		710,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		400,000		737,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost		23,343,000
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value		23,657,000
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost		5,595,000
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value		5,237,000
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost		12,112,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value		12,099,000
Commercial mortgage-backed securities guaranteed by U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		3,035,750,000		2,919,044,000
Available-for-sale Securities, Fair Value		3,017,933,000		2,905,796,000
Available-for-sale Securities, Gross Unrealized Gain		5,472,000	[1]	5,396,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(23,289,000)	[1]	(18,644,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		0	[3]	$ 0	[4]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		31,910,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		921,981,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		1,832,535,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		249,324,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		3,035,750,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less Than One Year, Fair Value		31,856,000
Available-for-sale Securities, Debt Maturities, One to Five Years, Fair Value		920,108,000
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Fair Value		1,820,627,000
Available-for-sale Securities, Debt Maturities, Over Ten Years, Fair Value		245,342,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 3,017,933,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Nominal Yield		1.00%
Available-for-sale Securities, Debt Maturities, One to Five Years, Nominal Yield		1.79%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield		1.85%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield		1.82%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.81%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[5]	6.90
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		171		213
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		$ 1,904,584,000		$ 1,582,469,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		38,875,000		484,258,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,943,459,000		2,066,727,000
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		22,987,000		11,419,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		302,000		7,225,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		23,289,000		18,644,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost		3,035,750,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value		3,017,933,000
Other debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		4,400,000		4,400,000
Available-for-sale Securities, Fair Value		4,152,000		4,151,000
Available-for-sale Securities, Gross Unrealized Gain		0	[1]	0	[2]
Available-for-sale Securities, Gross Unrealized Loss		(248,000)	[1]	(249,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		0	[3]	$ 0	[4]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, Less than One Year, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, One to Five Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Amortized Cost		0
Available-for-sale Securities, Debt Maturities, Over Ten Years, Amortized Cost		4,400,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis		4,400,000
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		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		4,152,000
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Fair value		$ 4,152,000
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		0.00%
Available-for-sale Securities, Debt Maturities, Six to Ten Years, Nominal Yield		0.00%
Available-for-sale Securities, Debt Maturities, Greater Than Ten Years, Nominal Yield		1.71%
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.71%
Available-for-sale Securities, Debt Maturities, Weighted Average Maturity	[5]	30.66
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		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
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		4,152,000		4,151,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		4,152,000		4,151,000
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		248,000		249,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		248,000		249,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost		4,400,000
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value		4,152,000
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value		0
Residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		5,576,543,000		5,989,207,000
Available-for-sale Securities, Fair Value		5,575,921,000		6,037,469,000
Available-for-sale Securities, Gross Unrealized Gain		50,377,000	[1]	70,448,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(50,781,000)	[1]	(21,359,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		(218,000)	[3]	$ (827,000)	[4]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis		5,576,543,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair value		$ 5,575,921,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield		1.86%
Available-for-sale Securities, Debt Maturities, Average Expected Life of Mortgage-backed Securities		3 years 10 months 8 days
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		186		122
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		$ 3,308,229,000		$ 2,279,654,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		129,716,000		215,636,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		3,437,945,000		2,495,290,000
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		47,767,000		17,040,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		3,232,000		5,146,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		50,999,000		22,186,000
U.S. government agency residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		5,475,351,000	[8]	5,861,096,000
Available-for-sale Securities, Fair Value		5,460,386,000	[8]	5,898,351,000
Available-for-sale Securities, Gross Unrealized Gain		35,800,000	[1]	58,614,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(50,765,000)	[1]	(21,359,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0	[3]	$ 0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		180		110
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		$ 3,300,298,000		$ 2,279,654,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		116,208,000		197,890,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		3,416,506,000		2,477,544,000
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		47,593,000		17,040,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		3,172,000		4,319,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		50,765,000		21,359,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost	[8]	0
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value	[8]	0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost	[8]	0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value	[8]	0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost	[8]	0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value	[8]	0
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost	[8]	5,475,351,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value	[8]	5,460,386,000
U.S. government agency residential mortgage-backed securities [Member] | FNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		3,062,525,000		3,156,214,000
Available-for-sale Securities, Fair Value		3,055,676,000		3,187,215,000
Available-for-sale Securities, Gross Unrealized Gain		25,066,000	[1]	41,502,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(31,915,000)	[1]	(10,501,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0	[3]	$ 0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		91		55
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		$ 1,787,644,000		$ 1,188,022,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		72,105,000		18,236,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,859,749,000		1,206,258,000
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		30,238,000		10,262,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		1,677,000		239,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		31,915,000		10,501,000
U.S. government agency residential mortgage-backed securities [Member] | FHLMC [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		1,534,451,000		1,940,915,000
Available-for-sale Securities, Fair Value		1,531,116,000		1,949,335,000
Available-for-sale Securities, Gross Unrealized Gain		8,475,000	[1]	14,727,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(11,810,000)	[1]	(6,307,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0	[3]	$ 0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		58		40
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		$ 964,017,000		$ 726,713,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		18,307,000		77,545,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		982,324,000		804,258,000
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		11,210,000		4,827,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		600,000		1,480,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		11,810,000		6,307,000
U.S. government agency residential mortgage-backed securities [Member] | GNMA [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		878,375,000		763,967,000
Available-for-sale Securities, Fair Value		873,594,000		761,801,000
Available-for-sale Securities, Gross Unrealized Gain		2,259,000	[1]	2,385,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(7,040,000)	[1]	(4,551,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0	[3]	$ 0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		31		15
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		$ 548,637,000		$ 364,919,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		25,796,000		102,109,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		574,433,000		467,028,000
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		6,145,000		1,951,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		895,000		2,600,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		7,040,000		4,551,000
Privately issued residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		101,192,000		128,111,000
Available-for-sale Securities, Fair Value		115,535,000		139,118,000
Available-for-sale Securities, Gross Unrealized Gain		14,577,000	[1]	11,834,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(16,000)	[1]	0	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ (218,000)	[3]	$ (827,000)	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		6	[9]	12	[10]
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		$ 7,931,000	[9]	$ 0	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		13,508,000	[9]	17,746,000	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		21,439,000	[9]	17,746,000	[10]
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		174,000	[9]	0	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		60,000	[9]	827,000	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		234,000	[9]	$ 827,000	[10]
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost		101,192,000
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value		115,535,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value		$ 0
Other Than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Assumptions Used to Develop Projected Cash Flows [Abstract]
Unemployment rate		Decreasing to 4.6% over the next 12 months and remain at 4.6% thereafter.		Decreasing to 4.8% over the next 12 months and remain at 4.8% thereafter.
Housing price appreciation/depreciation	[11]	Starting with current depreciated housing prices based on information derived from the FHFA1, appreciating 3.1% over the next 12 months, then flat for the following 12 months and then appreciating at 2% per year thereafter.		Starting with current depreciated housing prices based on information derived from the FHFA1, appreciating 3.5% over the next 12 months, then flat for the following 12 months and then appreciating at 2% per year thereafter.
Estimated liquidation costs		Reflect actual historical liquidations costs observed on Jumbo and Alt-A residential mortgage loans in securities owned by the Company.		Reflect actual historical liquidations costs observed on Jumbo and Alt-A residential mortgage loans in securities owned by the Company.
Discount rates		Estimated cash flows were discounted at rates that range from 2.00% to 6.25% based on our current expected yields.		Estimated cash flows were discounted at rates that range from 2.00% to 6.25% based on our current expected yields.
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net [Abstract]
Available-for-sale Securities, Other than Temporary Impairment Losses		$ 0		$ (157,000)		0
Privately issued residential mortgage-backed securities [Member] | Alt A [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		44,245,000		56,387,000
Available-for-sale Securities, Fair Value		51,512,000		62,574,000
Available-for-sale Securities, Gross Unrealized Gain		7,485,000	[1]	6,574,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		0	[1]	0	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ (218,000)	[3]	$ (387,000)	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		5	[9]	4	[10]
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		$ 7,931,000	[9]	$ 0	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		7,410,000	[9]	9,264,000	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		15,341,000	[9]	9,264,000	[10]
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		174,000	[9]	0	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		44,000	[9]	387,000	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		218,000	[9]	387,000	[10]
Privately issued residential mortgage-backed securities [Member] | Jumbo A Loans [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		56,947,000		71,724,000
Available-for-sale Securities, Fair Value		64,023,000		76,544,000
Available-for-sale Securities, Gross Unrealized Gain		7,092,000	[1]	5,260,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(16,000)	[1]	0	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0	[3]	$ (440,000)	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		1	[9]	8	[10]
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	[9]	$ 0	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		6,098,000	[9]	8,482,000	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		6,098,000	[9]	8,482,000	[10]
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	[9]	0	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		16,000	[9]	440,000	[10]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		16,000	[9]	440,000	[10]
Perpetual Preferred, Equity Securities and Mutual Funds [Member]
Available-for-sale Securities, Debt Maturities, Amortized Cost, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis		32,985,000
Available-for-sale Securities, Debt Maturities, Fair Value, Rolling Maturity [Abstract]
Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair value		$ 36,831,000
Available-for-sale Securities, Debt Maturities, Nominal Yield [Abstract]
Available-for-sale Securities, Debt Maturities, Nominal Yield		0.00%
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net [Abstract]
Available-for-sale Securities, Other than Temporary Impairment Losses		$ 0		(1,700,000)		$ (373,000)
Perpetual preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		15,561,000		17,171,000
Available-for-sale Securities, Fair Value		18,474,000		19,672,000
Available-for-sale Securities, Gross Unrealized Gain		2,913,000	[1]	2,501,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		0	[1]	0	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0	[3]	$ 0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		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
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost		4,796,000
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value		5,177,000
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost		10,765,000
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value		13,297,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value		0
Equity securities and mutual funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost		17,424,000		17,121,000
Available-for-sale Securities, Fair Value		18,357,000		17,833,000
Available-for-sale Securities, Gross Unrealized Gain		1,060,000	[1]	752,000	[2]
Available-for-sale Securities, Gross Unrealized Loss		(127,000)	[1]	(40,000)	[2]
Available-for-Sale Securities, Other Than Temporary Impairments		$ 0	[3]	$ 0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Securities		104		61
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		$ 2,127,000		$ 782,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		817,000		991,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,944,000		1,773,000
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		41,000		5,000
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		86,000		35,000
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		127,000		$ 40,000
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized In Earnings, Net Qualitative Disclosures, Lowest Current Credit Rating [Abstract]
Available-for-sale securities, Portfolio Concentration Rated AAA To AA, Amortized Cost		4,000
Available-for-sale Securities, Portfolio Concentration Rated AAA To AA, Fair Value		759,000
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated A To BBB, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Amortized Cost		0
Available-for-sale Securities, Portfolio Concentration Rated Below Investment Grade, Fair Value		0
Available-for-sale Securities, Portfolio Concentration Not Rated, Amortized Cost		17,420,000
Available-for-sale Securities, Portfolio Concentration Not Rated, Fair Value		$ 17,598,000

[1] Gross unrealized gain/loss recognized in AOCI in the consolidated balance sheet.

[2] Gross unrealized gain/loss recognized in AOCI in the consolidated balance sheet.

[3] Amounts represent unrealized loss that remains in AOCI after an other-than-temporary credit loss has been recognized in income.

[4] Amounts represent unrealized loss that remains in AOCI after an other-than-temporary credit loss has been recognized in income.

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

[6] Calculated on a taxable equivalent basis using a 39% effective tax rate.

[7] 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.

[8] U.S. government and government sponsored enterprises are not rated by the nationally-recognized rating agencies as these securities are guaranteed by agencies of the U.S. government or government-sponsored enterprises.

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

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

[11] Federal Housing Finance Agency