Investments (Summary Of Aggregate Market Value And Gross Unrealized Depreciation Of Fixed Maturity And Equity Securities, By Contractual Maturity) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Fixed maturity securities, Duration of Unrealized Loss, 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, Duration of Unrealized Loss, 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, Duration of Unrealized Loss, 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, Duration of Unrealized Loss, 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)
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	29,737	98,021
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(1,840)	(5,166)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	74,615	80,002
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(13,440)	(8,174)
Fixed maturity securities, Total, Market Value	104,352	178,023
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(15,280)	(13,340)
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	2,328,805	1,233,244
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(62,329)	(68,124)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	651,228	518,613
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(59,993)	(12,761)
Fixed maturity securities, Total, Market Value	2,980,033	1,751,857
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(122,322)	(80,885)
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	969,139	679,374
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(52,725)	(28,529)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	206,538	187,717
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(28,018)	(10,734)
Fixed maturity securities, Total, Market Value	1,175,677	867,091
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(80,743)	(39,263)
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	85,193	72,436
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(6,829)	(6,172)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	25,727	50,518
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(5,493)	(4,116)
Fixed maturity securities, Total, Market Value	110,920	122,954
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	(12,322)	(10,288)
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	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, Duration of Unrealized Loss, 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)
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	1,167,032	169,998
Fixed maturity securities, Duration of Unrealized loss, less than 12 months, Gross Unrealized Depreciation	(13,391)	(295)
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Market Value	326,487	689,015
Fixed maturity securities, Duration of Unrealized Loss, Greater than 12 months, Gross Unrealized Depreciation	(8,089)	(11,764)
Fixed maturity securities, Total, Market Value	1,493,519	859,013
Fixed maturity securities, Duration of Unrealized Loss, Total, Gross Unrealized Depreciation, Total	$ (21,480)	$ (12,059)