Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Security Type) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
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	$ 1,966,968	$ 1,730,364
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(68,531)	(26,793)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	831,126	1,909,627
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(100,856)	(94,376)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	2,798,094	3,639,991
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(169,387)	(121,169)
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	28,192	85,527
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(282)	(1,005)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value		249,371
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation		(1,209)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	28,192	334,898
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(282)	(2,214)
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	71,054	4,600
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(3,569)	(38)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	3,331	5,522
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(225)	(51)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	74,385	10,122
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(3,794)	(89)
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	712,066	547,120
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(28,954)	(9,877)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	170,908	395,369
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(37,338)	(27,890)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	882,974	942,489
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(66,292)	(37,767)
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	457,430	176,222
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(16,504)	(1,027)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	138,272	94,190
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(7,314)	(831)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	595,702	270,412
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(23,818)	(1,858)
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	47,046	83,127
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(1,196)	(689)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	6,017	23,063
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(641)	(560)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	53,063	106,190
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(1,837)	(1,249)
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	137,030	344,267
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(1,067)	(1,834)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	90,425	488,680
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(976)	(9,045)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	227,455	832,947
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(2,043)	(10,879)
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	213	332
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(3)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	2,898	3,976
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(39)	(20)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	3,111	4,308
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(42)	(20)
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	112,183	210,766
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(6,363)	(4,770)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	201,603	283,648
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(27,574)	(28,743)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	313,786	494,414
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(33,937)	(33,513)
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	401,754	278,403
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(10,593)	(7,553)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	217,672	365,808
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(26,749)	(26,027)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	619,426	644,211
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (37,342)	$ (33,580)