Investments (Summary Of Unrealized Appreciation (Depreciation) Of Available For Sale, Fixed Maturity And Equity Security Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 13,754,572		$ 12,733,499
Allowance for credit loss	(27,274)	$ (29,140)	(27,491)	$ (23,783)	$ (8,708)	$ (1,566)
Fixed maturities, available for sale, fair value	12,873,421		12,860,395
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,754,572		12,733,499
Allowance for credit loss	(27,274)		(27,491)
Unrealized Appreciation	31,338		240,516
Unrealized Depreciation	(885,215)		(86,129)
Fixed maturities, available for sale, fair value	12,873,421		12,860,395
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	615,312		656,742
Allowance for credit loss
Unrealized Appreciation	618		9,303
Unrealized Depreciation	(26,187)		(3,296)
Fixed maturities, available for sale, fair value	589,743		662,749
Obligation of U.S. States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	528,830		558,842
Allowance for credit loss	(151)	(151)	(151)
Unrealized Appreciation	3,951		29,080
Unrealized Depreciation	(24,349)		(1,150)
Fixed maturities, available for sale, fair value	508,281		586,621
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,355,517		4,036,000
Allowance for credit loss	(25,584)	(20,049)	(19,267)	(18,475)	(3,588)	(1,205)
Unrealized Appreciation	15,127		89,172
Unrealized Depreciation	(337,377)		(31,000)
Fixed maturities, available for sale, fair value	4,007,683		4,074,905
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,928,582		3,464,248
Allowance for credit loss		(7,680)	(7,680)	(4,915)	(4,915)
Unrealized Appreciation	679		20,732
Unrealized Depreciation	(177,890)		(11,014)
Fixed maturities, available for sale, fair value	3,751,371		3,466,286
Commercial [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	566,417		586,441
Allowance for credit loss
Unrealized Appreciation			20,538
Unrealized Depreciation	(41,999)		(4,085)
Fixed maturities, available for sale, fair value	524,418		602,894
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,522,073		1,255,186
Allowance for credit loss
Unrealized Appreciation	185		15,568
Unrealized Depreciation	(112,358)		(10,076)
Fixed maturities, available for sale, fair value	1,409,900		1,260,678
Non-agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,536		4,398
Allowance for credit loss
Unrealized Appreciation			16
Unrealized Depreciation	(143)		(6)
Fixed maturities, available for sale, fair value	3,393		4,408
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	697,135		677,327
Allowance for credit loss
Unrealized Appreciation	6,339		21,658
Unrealized Depreciation	(38,860)		(7,005)
Fixed maturities, available for sale, fair value	664,614		691,980
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,537,170		1,494,315
Allowance for credit loss	(1,539)	$ (1,260)	(393)	$ (393)	$ (205)	$ (361)
Unrealized Appreciation	4,439		34,449
Unrealized Depreciation	(126,052)		(18,497)
Fixed maturities, available for sale, fair value	$ 1,414,018		$ 1,509,874