Investments (Summary Of Unrealized Appreciation (Depreciation) Of Available For Sale, Fixed Maturity And Equity Security Investments) (Details) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 13,480,045	$ 13,276,206
Unrealized Appreciation		442,995	337,048
Unrealized Depreciation		(161,388)	(255,960)
Market Value		13,761,652	13,357,294
OTTI in AOCI	[1]	1,710	1,501
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		891,944	805,273
Unrealized Appreciation		27,721	13,465
Unrealized Depreciation		(153)	(1,861)
Market Value		919,512	816,877
Obligations Of U.S. States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		664,481	669,945
Unrealized Appreciation		38,439	34,020
Unrealized Depreciation		(843)	(890)
Market Value		702,077	703,075
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		4,733,277	4,817,014
Unrealized Appreciation		137,455	97,159
Unrealized Depreciation		(58,694)	(109,310)
Market Value		4,812,038	4,804,863
OTTI in AOCI	[1]	1,303	1,412
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		514,550	470,320
Unrealized Appreciation		2,623	719
Unrealized Depreciation		(1,454)	(3,813)
Market Value		515,719	467,226
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		269,123	264,924
Unrealized Appreciation		5,893	4,750
Unrealized Depreciation		(1,998)	(3,375)
Market Value		273,018	266,299
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,435,511	2,313,265
Unrealized Appreciation		41,982	25,318
Unrealized Depreciation		(4,204)	(18,059)
Market Value		2,473,289	2,320,524
Non-Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		836	893
Unrealized Appreciation		46	51
Unrealized Depreciation		(46)	(46)
Market Value		836	898
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,301,579	1,256,983
Unrealized Appreciation		65,835	54,403
Unrealized Depreciation		(44,671)	(52,205)
Market Value		1,322,743	1,259,181
OTTI in AOCI	[1]	39	53
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,668,744	2,677,589
Unrealized Appreciation		123,001	107,163
Unrealized Depreciation		(49,325)	(66,401)
Market Value		2,742,420	2,718,351
OTTI in AOCI	[1]	368	36
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		123,354	122,271
Unrealized Appreciation		4,008	3,401
Unrealized Depreciation		(12,974)	(16,732)
Market Value		$ 114,388	$ 108,940

[1] Represents the amount of OTTI recognized in AOCI. Amount includes unrealized gains and losses on impaired securities relating to changes in the value of such securities subsequent to the impairment measurement date