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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	Sep. 30, 2021	Dec. 31, 2020
AFS Fair Value, Less than 12 Months	$ 984,751	$ 415,506
AFS Unrealized Losses, Less than 12 months	(9,904)	(6,108)
AFS Fair Value, 12 months or longer	68,027	185,335
AFS Unrealized Losses, 12 months or longer	(990)	(5,434)
AFS Fair Value	1,052,778	600,841
AFS Unrealized Losses	(10,894)	(11,542)
U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 Months	34,717	11,519
AFS Unrealized Losses, Less than 12 months	(940)	(137)
AFS Fair Value, 12 months or longer	156	0
AFS Unrealized Losses, 12 months or longer	(17)	0
AFS Fair Value	34,873	11,519
AFS Unrealized Losses	(957)	(137)
Foreign Government [Member]
AFS Fair Value, Less than 12 Months	3,114	1,122
AFS Unrealized Losses, Less than 12 months	(75)	(3)
AFS Fair Value, 12 months or longer	0	0
AFS Unrealized Losses, 12 months or longer	0	0
AFS Fair Value	3,114	1,122
AFS Unrealized Losses	(75)	(3)
Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 Months	7,936	2,223
AFS Unrealized Losses, Less than 12 months	(103)	(11)
AFS Fair Value, 12 months or longer	0	0
AFS Unrealized Losses, 12 months or longer	0	0
AFS Fair Value	7,936	2,223
AFS Unrealized Losses	(103)	(11)
Corporate Securities [Member]
AFS Fair Value, Less than 12 Months	236,164	65,187
AFS Unrealized Losses, Less than 12 months	(3,067)	(2,152)
AFS Fair Value, 12 months or longer	2,412	2,400
AFS Unrealized Losses, 12 months or longer	(34)	(188)
AFS Fair Value	238,576	67,587
AFS Unrealized Losses	(3,101)	(2,340)
Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 Months	515,458	261,746
AFS Unrealized Losses, Less than 12 months	(3,723)	(2,995)
AFS Fair Value, 12 months or longer	57,153	165,661
AFS Unrealized Losses, 12 months or longer	(794)	(4,848)
AFS Fair Value	572,611	427,407
AFS Unrealized Losses	(4,517)	(7,843)
Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	111,648	18,227
AFS Unrealized Losses, Less than 12 months	(1,055)	(194)
AFS Fair Value, 12 months or longer	20	1,181
AFS Unrealized Losses, 12 months or longer	(1)	(7)
AFS Fair Value	111,668	19,408
AFS Unrealized Losses	(1,056)	(201)
Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	75,714	55,482
AFS Unrealized Losses, Less than 12 months	(941)	(616)
AFS Fair Value, 12 months or longer	8,286	16,093
AFS Unrealized Losses, 12 months or longer	(144)	(391)
AFS Fair Value	84,000	71,575
AFS Unrealized Losses	$ (1,085)	$ (1,007)

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