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, 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	$ 2,009,793	$ 1,730,364
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(56,698)	(26,793)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	809,252	1,909,627
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(89,879)	(94,376)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	2,819,045	3,639,991
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(146,577)	(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	69,055	85,527
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(3,023)	(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	69,055	334,898
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(3,023)	(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	50,368	4,600
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(2,278)	(38)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	4,943	5,522
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(165)	(51)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	55,311	10,122
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(2,443)	(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	752,828	547,120
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(24,799)	(9,877)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	196,660	395,369
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(42,118)	(27,890)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	949,488	942,489
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(66,917)	(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	328,216	176,222
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(8,346)	(1,027)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	163,014	94,190
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(3,561)	(831)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	491,230	270,412
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(11,907)	(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	77,850	83,127
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(1,524)	(689)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	6,634	23,063
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(452)	(560)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	84,484	106,190
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(1,976)	(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	248,155	344,267
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(1,256)	(1,834)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	65,145	488,680
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(1,212)	(9,045)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	313,300	832,947
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(2,468)	(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	2,308	3,976
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(36)	(20)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	2,521	4,308
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(39)	(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	83,267	210,766
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(4,352)	(4,770)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	176,739	283,648
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(22,561)	(28,743)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	260,006	494,414
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(26,913)	(33,513)
Foreign Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	399,841	278,403
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(11,117)	(7,553)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	193,809	365,808
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(19,774)	(26,027)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	593,650	644,211
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (30,891)	$ (33,580)