Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Security Type) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	$ 5,142,592	$ 2,017,481
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(108,337)	(67,958)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	886,529	660,968
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(45,765)	(56,854)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	6,029,121	2,678,449
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(154,102)	(124,812)
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	381,357	135,190
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(6,369)	(7,134)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	57,084
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(3,954)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	438,441	135,190
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(10,323)	(7,134)
Obligations Of U.S. States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	61,687	19,524
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(937)	(999)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	3,569	4,059
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(121)	(255)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	65,256	23,583
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(1,058)	(1,254)
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	1,559,623	669,755
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(32,541)	(26,159)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	399,617	247,962
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(20,195)	(29,072)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	1,959,240	917,717
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(52,736)	(55,231)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	610,425	235,566
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(3,131)	(4,768)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	23,396	85,595
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(368)	(930)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	633,821	321,161
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(3,499)	(5,698)
Mortgage-Backed Securities: Commercial [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	108,367	53,511
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(3,138)	(578)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	26,144	6,592
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(1,225)	(317)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	134,511	60,103
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(4,363)	(895)
Mortgage Backed Securities: Agency residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	814,318	434,447
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(5,631)	(2,016)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	134,746	50,353
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(2,784)	(1,047)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	949,064	484,800
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(8,415)	(3,063)
Mortgage Backed Securities: Non-agency residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	2,742	185
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(19)	(2)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	156
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(2)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	2,898	185
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(21)	(2)
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	382,570	114,755
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(22,491)	(8,813)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	58,238	150,812
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(5,247)	(13,637)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	440,808	265,567
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(27,738)	(22,450)
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	1,221,503	354,548
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(34,080)	(17,489)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	183,579	115,595
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(11,869)	(11,596)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	1,405,082	470,143
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (45,949)	$ (29,085)

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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