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Investments (Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time) (Details) - Available-for-sale Securities - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
AFS Fair Value, Less than 12 Months	$ 4,657,248	$ 1,376,128
AFS Unrealized Losses, Less than 12 months	(335,523)	(14,849)
AFS Fair Value, 12 months or longer	225,652	85,122
AFS Unrealized Losses, 12 months or longer	(22,174)	(2,505)
AFS Fair Value	4,882,900	1,461,250
AFS Unrealized Losses	(357,697)	(17,354)
U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 Months	89,797	34,857
AFS Unrealized Losses, Less than 12 months	(9,864)	(746)
AFS Fair Value, 12 months or longer	4,522	7,827
AFS Unrealized Losses, 12 months or longer	(1,532)	(399)
AFS Fair Value	94,319	42,684
AFS Unrealized Losses	(11,396)	(1,145)
Foreign Government [Member]
AFS Fair Value, Less than 12 Months	11,027	2,000
AFS Unrealized Losses, Less than 12 months	(962)	(84)
AFS Fair Value, 12 months or longer	1,799	1,061
AFS Unrealized Losses, 12 months or longer	(376)	(39)
AFS Fair Value	12,826	3,061
AFS Unrealized Losses	(1,338)	(123)
Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 Months	466,743	25,837
AFS Unrealized Losses, Less than 12 months	(31,280)	(235)
AFS Fair Value, 12 months or longer	2,875	0
AFS Unrealized Losses, 12 months or longer	(278)	0
AFS Fair Value	469,618	25,837
AFS Unrealized Losses	(31,558)	(235)
Corporate Securities [Member]
AFS Fair Value, Less than 12 Months	1,649,434	300,549
AFS Unrealized Losses, Less than 12 months	(152,902)	(4,903)
AFS Fair Value, 12 months or longer	6,839	2,520
AFS Unrealized Losses, 12 months or longer	(1,302)	(50)
AFS Fair Value	1,656,273	303,069
AFS Unrealized Losses	(154,204)	(4,953)
Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 Months	1,114,978	663,976
AFS Unrealized Losses, Less than 12 months	(68,918)	(4,934)
AFS Fair Value, 12 months or longer	158,322	53,368
AFS Unrealized Losses, 12 months or longer	(11,581)	(1,350)
AFS Fair Value	1,273,300	717,344
AFS Unrealized Losses	(80,499)	(6,284)
Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	813,811	236,010
AFS Unrealized Losses, Less than 12 months	(47,346)	(2,931)
AFS Fair Value, 12 months or longer	17,605	20
AFS Unrealized Losses, 12 months or longer	(2,839)	(1)
AFS Fair Value	831,416	236,030
AFS Unrealized Losses	(50,185)	(2,932)
Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	511,458	112,899
AFS Unrealized Losses, Less than 12 months	(24,251)	(1,016)
AFS Fair Value, 12 months or longer	33,690	20,326
AFS Unrealized Losses, 12 months or longer	(4,266)	(666)
AFS Fair Value	545,148	133,225
AFS Unrealized Losses	$ (28,517)	$ (1,682)

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