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, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	$ 1,756,495	$ 4,928,451
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(67,675)	(139,624)
Fixed maturity securities, Greater than 12 months, Market Value	1,292,635	1,443,732
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(106,687)	(133,068)
Fixed maturity securities, Total, Market Value	3,049,130	6,372,183
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(174,362)	(272,692)
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	1,756,495	4,928,451
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(67,675)	(139,624)
Fixed maturity securities, Greater than 12 months, Market Value	1,195,864	1,351,825
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(93,713)	(116,336)
Fixed maturity securities, Total, Market Value	2,952,359	6,280,276
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(161,388)	(255,960)
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, Less than 12 months, Market Value	71,914	539,177
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(153)	(1,855)
Fixed maturity securities, Greater than 12 months, Market Value	698	692
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation		(6)
Fixed maturity securities, Total, Market Value	72,612	539,869
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(153)	(1,861)
Obligations Of U.S. States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	4,469	6,434
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(16)	(84)
Fixed maturity securities, Greater than 12 months, Market Value	7,014	4,917
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(827)	(806)
Fixed maturity securities, Total, Market Value	11,483	11,351
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(843)	(890)
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	757,686	1,818,331
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(29,211)	(74,161)
Fixed maturity securities, Greater than 12 months, Market Value	340,682	440,682
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(29,483)	(35,149)
Fixed maturity securities, Total, Market Value	1,098,368	2,259,013
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(58,694)	(109,310)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	66,629	348,545
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(257)	(2,510)
Fixed maturity securities, Greater than 12 months, Market Value	68,896	67,230
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(1,197)	(1,303)
Fixed maturity securities, Total, Market Value	135,525	415,775
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(1,454)	(3,813)
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	33,955	145,490
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(1,707)	(3,375)
Fixed maturity securities, Greater than 12 months, Market Value	6,345
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(291)
Fixed maturity securities, Total, Market Value	40,300	145,490
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(1,998)	(3,375)
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	239,830	1,021,390
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(1,726)	(10,014)
Fixed maturity securities, Greater than 12 months, Market Value	290,778	326,449
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(2,478)	(8,045)
Fixed maturity securities, Total, Market Value	530,608	1,347,839
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(4,204)	(18,059)
Non-Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	137	152
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(2)	(2)
Fixed maturity securities, Greater than 12 months, Market Value	34	38
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(44)	(44)
Fixed maturity securities, Total, Market Value	171	190
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(46)	(46)
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	167,643	227,384
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(18,658)	(21,996)
Fixed maturity securities, Greater than 12 months, Market Value	196,372	216,428
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(26,013)	(30,209)
Fixed maturity securities, Total, Market Value	364,015	443,812
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(44,671)	(52,205)
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	414,232	821,548
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(15,945)	(25,627)
Fixed maturity securities, Greater than 12 months, Market Value	285,045	295,389
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(33,380)	(40,774)
Fixed maturity securities, Total, Market Value	699,277	1,116,937
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(49,325)	(66,401)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Greater than 12 months, Market Value	96,771	91,907
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(12,974)	(16,732)
Fixed maturity securities, Total, Market Value	96,771	91,907
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (12,974)	$ (16,732)