Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Security Type) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	$ 4,928,451	$ 2,495,611
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(139,624)	(113,584)
Fixed maturity securities, Greater than 12 months, Market Value	1,443,732	1,599,859
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(133,068)	(55,428)
Fixed maturity securities, Total, Market Value	6,372,183	4,095,470
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(272,692)	(169,012)
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	4,928,451	2,445,326
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(139,624)	(109,516)
Fixed maturity securities, Greater than 12 months, Market Value	1,351,825	1,525,865
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(116,336)	(47,549)
Fixed maturity securities, Total, Market Value	6,280,276	3,971,191
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(255,960)	(157,065)
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	539,177	13,187
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(1,855)	(20)
Fixed maturity securities, Greater than 12 months, Market Value	692	26,897
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(6)	(284)
Fixed maturity securities, Total, Market Value	539,869	40,084
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(1,861)	(304)
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	6,434	20,428
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(84)	(242)
Fixed maturity securities, Greater than 12 months, Market Value	4,917	18,199
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(806)	(384)
Fixed maturity securities, Total, Market Value	11,351	38,627
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(890)	(626)
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	1,818,331	1,245,830
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(74,161)	(55,388)
Fixed maturity securities, Greater than 12 months, Market Value	440,682	362,320
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(35,149)	(7,518)
Fixed maturity securities, Total, Market Value	2,259,013	1,608,150
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(109,310)	(62,906)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	348,545	192,253
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(2,510)	(1,230)
Fixed maturity securities, Greater than 12 months, Market Value	67,230
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(1,303)
Fixed maturity securities, Total, Market Value	415,775	192,253
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(3,813)	(1,230)
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	145,490	28,191
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(3,375)	(123)
Fixed maturity securities, Greater than 12 months, Market Value		9,777
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation		(306)
Fixed maturity securities, Total, Market Value	145,490	37,968
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(3,375)	(429)
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	1,021,390	141,807
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(10,014)	(172)
Fixed maturity securities, Greater than 12 months, Market Value	326,449	678,972
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(8,045)	(11,401)
Fixed maturity securities, Total, Market Value	1,347,839	820,779
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(18,059)	(11,573)
Non-Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	152
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(2)
Fixed maturity securities, Greater than 12 months, Market Value	38	266
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(44)	(57)
Fixed maturity securities, Total, Market Value	190	266
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(46)	(57)
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	227,384	235,725
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(21,996)	(15,415)
Fixed maturity securities, Greater than 12 months, Market Value	216,428	139,200
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(30,209)	(11,451)
Fixed maturity securities, Total, Market Value	443,812	374,925
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(52,205)	(26,866)
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value	821,548	567,905
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(25,627)	(36,926)
Fixed maturity securities, Greater than 12 months, Market Value	295,389	290,234
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(40,774)	(16,148)
Fixed maturity securities, Total, Market Value	1,116,937	858,139
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(66,401)	(53,074)
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Less than 12 months, Market Value		50,285
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation		(4,068)
Fixed maturity securities, Greater than 12 months, Market Value	91,907	73,994
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(16,732)	(7,879)
Fixed maturity securities, Total, Market Value	91,907	124,279
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (16,732)	$ (11,947)