Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Contractual Maturity) (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)
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	74,911	67,879
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(897)	(1,237)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	154,772	416,583
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(24,782)	(23,004)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	229,683	484,462
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(25,679)	(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	738,690	464,753
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(23,176)	(7,960)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	325,533	689,195
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(32,475)	(38,138)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	1,064,223	1,153,948
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(55,651)	(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	368,721	495,741
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(16,989)	(12,388)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	51,998	103,612
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(8,556)	(11,100)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	420,719	599,353
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(25,545)	(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	142,927	98,043
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(8,699)	(1,658)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	61,211	90,328
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(26,073)	(11,678)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	204,138	188,371
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(34,772)	(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	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)
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	184,289	427,726
Fixed maturity securities, Duration of Unrealized Loss, Less than 12 months, Gross Unrealized Depreciation	(2,266)	(2,523)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	99,340	515,719
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(1,656)	(9,625)
Fixed maturity securities, Duration of Unrealized Loss, Total, Market Value	283,629	943,445
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (3,922)	$ (12,148)