Investments (Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 Months	$ 208,153	$ 166,975
AFS Unrealized Losses, Less than 12 months	(2,831)	(13,658)
AFS Fair Value, 12 months or longer	84,869	16,011
AFS Unrealized Losses, 12 months or longer	(18,112)	(6,668)
AFS Fair Value	293,022	182,986
AFS Unrealized Losses	(20,943)	(20,326)
Foreign Government [Member]
AFS Fair Value, Less than 12 Months	4,380	5,573
AFS Unrealized Losses, Less than 12 months	(247)	(608)
AFS Fair Value, 12 months or longer	5,439	2,456
AFS Unrealized Losses, 12 months or longer	(1,071)	(699)
AFS Fair Value	9,819	8,029
AFS Unrealized Losses	(1,318)	(1,307)
Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 Months	337,606	681,795
AFS Unrealized Losses, Less than 12 months	(5,554)	(43,767)
AFS Fair Value, 12 months or longer	229,922	16,618
AFS Unrealized Losses, 12 months or longer	(31,990)	(4,234)
AFS Fair Value	567,528	698,413
AFS Unrealized Losses	(37,544)	(48,001)
Corporate Securities [Member]
AFS Fair Value, Less than 12 Months	1,101,756	1,889,492
AFS Unrealized Losses, Less than 12 months	(40,711)	(164,197)
AFS Fair Value, 12 months or longer	895,497	133,223
AFS Unrealized Losses, 12 months or longer	(148,953)	(32,612)
AFS Fair Value	1,997,253	2,022,715
AFS Unrealized Losses	(189,664)	(196,809)
Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 Months	523,727	916,423
AFS Unrealized Losses, Less than 12 months	(17,268)	(69,155)
AFS Fair Value, 12 months or longer	924,490	411,283
AFS Unrealized Losses, 12 months or longer	(88,689)	(52,565)
AFS Fair Value	1,448,217	1,327,706
AFS Unrealized Losses	(105,957)	(121,720)
Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	792,885	887,229
AFS Unrealized Losses, Less than 12 months	(26,269)	(76,432)
AFS Fair Value, 12 months or longer	538,073	108,041
AFS Unrealized Losses, 12 months or longer	(75,540)	(22,833)
AFS Fair Value	1,330,958	995,270
AFS Unrealized Losses	(101,809)	(99,265)
Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	291,078	512,953
AFS Unrealized Losses, Less than 12 months	(12,882)	(37,815)
AFS Fair Value, 12 months or longer	344,647	77,181
AFS Unrealized Losses, 12 months or longer	(42,162)	(11,945)
AFS Fair Value	635,725	590,134
AFS Unrealized Losses	(55,044)	(49,760)
Available-for-sale Securities [Member]
AFS Fair Value, Less than 12 Months	3,259,585	5,060,440
AFS Unrealized Losses, Less than 12 months	(105,762)	(405,632)
AFS Fair Value, 12 months or longer	3,022,937	764,813
AFS Unrealized Losses, 12 months or longer	(406,517)	(131,556)
AFS Fair Value	6,282,522	5,825,253
AFS Unrealized Losses	$ (512,279)	$ (537,188)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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