Investments (Summary Of Unrealized Appreciation (Depreciation) Of Available For Sale, Fixed Maturity And Equity Security Investments) (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Fixed Maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 6,071,568	$ 5,910,494
Unrealized Appreciation		118,371	126,510
Unrealized Depreciation		(49,911)	(66,508)
Market Value		6,140,028	5,970,496
OTTI in AOCI	[1]	1,227	5,043
U.S. Treasury Securities And Obligations Of U.S. Government Agencies And Corporations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		667,000	693,005
Unrealized Appreciation		2,961	2,509
Unrealized Depreciation		(3,184)	(4,434)
Market Value		666,777	691,080
OTTI in AOCI	[1]
Obligations of U.S. States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		679,940	723,938
Unrealized Appreciation		22,970	18,016
Unrealized Depreciation		(6,127)	(11,970)
Market Value		696,783	729,984
OTTI in AOCI	[1]
Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,274,212	2,119,324
Unrealized Appreciation		40,765	50,665
Unrealized Depreciation		(13,976)	(15,786)
Market Value		2,301,001	2,154,203
OTTI in AOCI	[1]	908	4,868
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		189,598	136,826
Unrealized Appreciation		433	330
Unrealized Depreciation		(42)	(129)
Market Value		189,989	137,027
OTTI in AOCI	[1]
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		73,127	75,435
Unrealized Appreciation		507	510
Unrealized Depreciation		(389)	(452)
Market Value		73,245	75,493
OTTI in AOCI	[1]
Agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		688,735	721,772
Unrealized Appreciation		2,163	2,365
Unrealized Depreciation		(7,217)	(8,993)
Market Value		683,681	715,144
OTTI in AOCI	[1]
Non-agency Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		61	76
Unrealized Appreciation		9	12
Unrealized Depreciation
Market Value		70	88
OTTI in AOCI	[1]
Foreign Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		489,750	495,572
Unrealized Appreciation		20,205	22,088
Unrealized Depreciation		(8,568)	(10,383)
Market Value		501,387	507,277
OTTI in AOCI	[1]
Foreign Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,009,145	944,546
Unrealized Appreciation		28,358	30,015
Unrealized Depreciation		(10,408)	(14,361)
Market Value		1,027,095	960,200
OTTI in AOCI	[1]	$ 319	$ 175

[1] (a) 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.