Investments In Fixed Maturity Securities Investments in Fixed Maturity Securities (Amortized cost and fair value of fixed maturity securities) (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment		$ 101,306	$ 101,177
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		(17,826)	(20,646)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		0	0
Held-to-maturity Securities, Fair Value		119,132	121,823
Held-to-maturity Securities		101,306	101,177
Available-for-sale Debt Securities, Amortized Cost Basis		11,917,655	12,122,087
Available For Sale Securities Debt Securities Gross Unrealized Gain		457,432	541,420
Available For Sale Securities Debt Securities Gross Unrealized Losses		(80,583)	(59,524)
Available For Sale Securities Debt Securities Fair Value		12,294,504	12,603,983
Available-for-sale Securities, Debt Securities		12,294,504	12,603,983
Marketable Securities Fixed Maturities Gross Unrealized Gains		475,258	562,066
Fixed maturity securities		12,395,810	12,705,160
Marketable Securities Fixed Maturities Gross Unrealized Losses		80,583	59,524
Amortized Cost, Due in one year or less		818,912
Amortized Cost, Due after one year through five years		3,934,376
Amortized Cost, Due after five years through ten years		3,612,449
Amortized Cost, Due after ten years		2,477,644
Amortized Cost, Mortgaged-backed securities		1,175,580
Total investments in fixed maturity securities, Amortized Value		12,018,961	12,223,264
Fair Value, Due in one year or less		825,584
Fair Value, Due after one year through five years		4,091,220
Fair Value, Due after five years through ten years		3,754,639
Fair Value, Due after ten years		2,549,014
Fair Value, Mortgage-backed securities		1,193,179
Total investments in fixed maturity securities, Fair Value		12,413,636	12,725,806
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		918,738	897,668
Available For Sale Securities Debt Securities Gross Unrealized Gain		65,344	62,223
Available For Sale Securities Debt Securities Gross Unrealized Losses		(16,932)	(18,065)
Available For Sale Securities Debt Securities Fair Value		967,150	941,826
Available-for-sale Securities, Debt Securities		967,150	941,826
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		68,378	74,479
Available For Sale Securities Debt Securities Gross Unrealized Gain		1,053	1,610
Available For Sale Securities Debt Securities Gross Unrealized Losses		(93)	(52)
Available For Sale Securities Debt Securities Fair Value		69,338	76,037
Available-for-sale Securities, Debt Securities		69,338	76,037
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	[1]	1,085,961	1,201,924
Available For Sale Securities Debt Securities Gross Unrealized Gain	[1]	24,498	27,124
Available For Sale Securities Debt Securities Gross Unrealized Losses	[1]	(10,514)	(9,449)
Available For Sale Securities Debt Securities Fair Value	[1]	1,099,945	1,219,599
Available-for-sale Securities, Debt Securities	[1]	1,099,945	1,219,599
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		4,133,971	4,137,866
Available For Sale Securities Debt Securities Gross Unrealized Gain		180,941	229,150
Available For Sale Securities Debt Securities Gross Unrealized Losses		(16,061)	(4,020)
Available For Sale Securities Debt Securities Fair Value		4,298,851	4,362,996
Available-for-sale Securities, Debt Securities		4,298,851	4,362,996
U.S. government and government agency
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		691,250	773,192
Available For Sale Securities Debt Securities Gross Unrealized Gain		27,672	33,353
Available For Sale Securities Debt Securities Gross Unrealized Losses		(3,555)	(3,157)
Available For Sale Securities Debt Securities Fair Value		715,367	803,388
Available-for-sale Securities, Debt Securities		715,367	803,388
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		2,345,401	2,264,210
Available For Sale Securities Debt Securities Gross Unrealized Gain		91,768	111,841
Available For Sale Securities Debt Securities Gross Unrealized Losses		(8,386)	(2,084)
Available For Sale Securities Debt Securities Fair Value		2,428,783	2,373,967
Available-for-sale Securities, Debt Securities		2,428,783	2,373,967
Debt, State Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		640,845	674,022
Available For Sale Securities Debt Securities Gross Unrealized Gain		25,694	37,615
Available For Sale Securities Debt Securities Gross Unrealized Losses		(6,113)	(787)
Available For Sale Securities Debt Securities Fair Value		660,426	710,850
Available-for-sale Securities, Debt Securities		660,426	710,850
Revenue Subject to Refund [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		444,165	504,778
Available For Sale Securities Debt Securities Gross Unrealized Gain		28,606	35,619
Available For Sale Securities Debt Securities Gross Unrealized Losses		(133)	(289)
Available For Sale Securities Debt Securities Fair Value		472,638	540,108
Available-for-sale Securities, Debt Securities		472,638	540,108
Corporation [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		419,572	413,234
Available For Sale Securities Debt Securities Gross Unrealized Gain		13,850	18,976
Available For Sale Securities Debt Securities Gross Unrealized Losses		(998)	(855)
Available For Sale Securities Debt Securities Fair Value		432,424	431,355
Available-for-sale Securities, Debt Securities		432,424	431,355
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		5,019,357	5,036,958
Available For Sale Securities Debt Securities Gross Unrealized Gain		157,924	187,960
Available For Sale Securities Debt Securities Gross Unrealized Losses		(33,428)	(24,781)
Available For Sale Securities Debt Securities Fair Value		5,143,853	5,200,137
Available-for-sale Securities, Debt Securities		5,143,853	5,200,137
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,154,339	1,276,403
Available For Sale Securities Debt Securities Gross Unrealized Gain		25,551	28,734
Available For Sale Securities Debt Securities Gross Unrealized Losses		(10,607)	(9,501)
Available For Sale Securities Debt Securities Fair Value		1,169,283	1,295,636
Available-for-sale Securities, Debt Securities		1,169,283	1,295,636
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,644,366	2,019,032
Available For Sale Securities Debt Securities Gross Unrealized Gain		17,816	18,868
Available For Sale Securities Debt Securities Gross Unrealized Losses		(10,027)	(11,974)
Available For Sale Securities Debt Securities Fair Value		1,652,155	2,025,926
Available-for-sale Securities, Debt Securities		1,652,155	2,025,926
Industrial Property [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,780,193	1,606,724
Available For Sale Securities Debt Securities Gross Unrealized Gain		96,890	117,206
Available For Sale Securities Debt Securities Gross Unrealized Losses		(10,238)	(5,131)
Available For Sale Securities Debt Securities Fair Value		1,866,845	1,718,799
Available-for-sale Securities, Debt Securities		1,866,845	1,718,799
Domestic Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,296,370	1,140,801
Available For Sale Securities Debt Securities Gross Unrealized Gain		32,050	38,080
Available For Sale Securities Debt Securities Gross Unrealized Losses		(10,412)	(7,673)
Available For Sale Securities Debt Securities Fair Value		1,318,008	1,171,208
Available-for-sale Securities, Debt Securities		1,318,008	1,171,208
Public Utility, Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		182,282	184,107
Available For Sale Securities Debt Securities Gross Unrealized Gain		10,412	12,436
Available For Sale Securities Debt Securities Gross Unrealized Losses		(2,212)	(1)
Available For Sale Securities Debt Securities Fair Value		190,482	196,542
Available-for-sale Securities, Debt Securities		190,482	196,542
Other Security Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		116,146	86,294
Available For Sale Securities Debt Securities Gross Unrealized Gain		756	1,370
Available For Sale Securities Debt Securities Gross Unrealized Losses		(539)	(2)
Available For Sale Securities Debt Securities Fair Value		116,363	87,662
Available-for-sale Securities, Debt Securities		116,363	87,662
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment		75,066	72,901
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		(15,029)	(17,501)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		0	0
Held-to-maturity Securities, Fair Value		90,095	90,402
Held-to-maturity Securities		75,066	72,901
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment		21,241	23,278
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		(2,655)	(2,854)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		0	0
Held-to-maturity Securities, Fair Value		23,896	26,132
Held-to-maturity Securities		21,241	23,278
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment		4,999	4,998
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		(142)	(291)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		0	0
Held-to-maturity Securities, Fair Value		5,141	5,289
Held-to-maturity Securities		$ 4,999	$ 4,998

[1] Gross unrealized losses for residential mortgage-backed securities include $1,073,002 and $1,095,671 as of June 30, 2015 and December 31, 2014, respectively, related to the non-credit portion of other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income.