Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Security Type) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value		$ 1,150,395
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total		(45,952)
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	$ 2,098,023	825,833
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(48,051)	(16,792)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	272,017	324,562
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(23,541)	(29,160)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	2,370,040	1,150,395
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(71,592)	(45,952)
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	38,242
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(167)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	38,242
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(167)
Obligation 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	56,822	19,524
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(1,710)	(999)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	12,079	4,059
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(1,031)	(256)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	68,901	23,583
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(2,741)	(1,255)
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	790,015	240,601
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(24,012)	(7,799)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	187,655	188,853
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(17,872)	(23,681)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	977,670	429,454
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(41,884)	(31,480)
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	240,987	223,919
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(1,749)	(4,573)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	22,773	81,952
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(461)	(649)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	263,760	305,871
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(2,210)	(5,222)
Commercial [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	120,334	37,414
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(5,158)	(182)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value		3,983
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation		(1)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	120,334	41,397
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(5,158)	(183)
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	529,830	235,809
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(8,000)	(682)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	12,012	1,573
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(153)	(14)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	541,842	237,382
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(8,153)	(696)
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	3,529	161
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation		(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	3,685	161
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(2)	(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	69,597	10,505
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(1,550)	(373)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	22,968	25,793
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(2,515)	(2,838)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	92,565	36,298
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(4,065)	(3,211)
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	248,667	57,900
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(5,705)	(2,182)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	14,374	18,349
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(1,507)	(1,721)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	263,041	76,249
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (7,212)	$ (3,903)