Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Contractual Maturity) (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)
Due In One Year Or Less [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	76,867	67,879
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(2,652)	(1,237)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	135,762	416,583
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(21,608)	(23,004)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	212,629	484,462
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(24,260)	(24,241)
Due In One Year Through Five Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	675,450	464,753
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(22,976)	(7,960)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	304,410	689,195
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(29,003)	(38,138)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	979,860	1,153,948
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(51,979)	(46,098)
Due In Five Years Through Ten Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	377,219	495,741
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(12,287)	(12,388)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	69,424	103,612
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(4,266)	(11,100)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	446,643	599,353
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(16,553)	(23,488)
Due After Ten Years [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Market Value	225,823	98,043
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(7,654)	(1,658)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	62,555	90,328
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(29,741)	(11,678)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	288,378	188,371
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(37,395)	(13,336)
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)
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	326,218	427,726
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(2,783)	(2,523)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	74,087	515,719
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(1,700)	(9,625)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	400,305	943,445
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (4,483)	$ (12,148)