Investments In Fixed Maturity Securities Investments in Fixed Maturity Securities (Amortized cost and fair value of fixed maturity securities) (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment		$ 101,090	$ 101,177
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		(18,526)	(20,646)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		0	0
Held-to-maturity Securities, Fair Value		119,616	121,823
Held-to-maturity Securities		101,090	101,177
Available-for-sale Debt Securities, Amortized Cost Basis		11,886,732	12,122,087
Available For Sale Securities Debt Securities Gross Unrealized Gain		457,919	541,420
Available For Sale Securities Debt Securities Gross Unrealized Losses		(77,422)	(59,524)
Available For Sale Securities Debt Securities Fair Value		12,267,229	12,603,983
Available-for-sale Securities, Debt Securities		12,267,229	12,603,983
Marketable Securities Fixed Maturities Gross Unrealized Gains		476,445	562,066
Fixed maturity securities		12,368,319	12,705,160
Marketable Securities Fixed Maturities Gross Unrealized Losses		77,422	59,524
Amortized Cost, Due in one year or less		872,912
Amortized Cost, Due after one year through five years		3,896,880
Amortized Cost, Due after five years through ten years		3,572,074
Amortized Cost, Due after ten years		2,520,025
Amortized Cost, Mortgaged-backed securities		1,125,931
Total investments in fixed maturity securities, Amortized Value		11,987,822	12,223,264
Fair Value, Due in one year or less		884,845
Fair Value, Due after one year through five years		4,043,852
Fair Value, Due after five years through ten years		3,706,649
Fair Value, Due after ten years		2,601,213
Fair Value, Mortgage-backed securities		1,150,286
Total investments in fixed maturity securities, Fair Value		12,386,845	12,725,806
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		854,313	897,668
Available For Sale Securities Debt Securities Gross Unrealized Gain		46,433	62,223
Available For Sale Securities Debt Securities Gross Unrealized Losses		(16,077)	(18,065)
Available For Sale Securities Debt Securities Fair Value		884,669	941,826
Available-for-sale Securities, Debt Securities		884,669	941,826
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		67,003	74,479
Available For Sale Securities Debt Securities Gross Unrealized Gain		1,236	1,610
Available For Sale Securities Debt Securities Gross Unrealized Losses		(35)	(52)
Available For Sale Securities Debt Securities Fair Value		68,204	76,037
Available-for-sale Securities, Debt Securities		68,204	76,037
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	[1]	1,038,903	1,201,924
Available For Sale Securities Debt Securities Gross Unrealized Gain	[1]	27,601	27,124
Available For Sale Securities Debt Securities Gross Unrealized Losses	[1]	(7,084)	(9,449)
Available For Sale Securities Debt Securities Fair Value	[1]	1,059,420	1,219,599
Available-for-sale Securities, Debt Securities	[1]	1,059,420	1,219,599
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		4,228,908	4,137,866
Available For Sale Securities Debt Securities Gross Unrealized Gain		205,114	229,150
Available For Sale Securities Debt Securities Gross Unrealized Losses		(10,265)	(4,020)
Available For Sale Securities Debt Securities Fair Value		4,423,757	4,362,996
Available-for-sale Securities, Debt Securities		4,423,757	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		641,696	773,192
Available For Sale Securities Debt Securities Gross Unrealized Gain		32,748	33,353
Available For Sale Securities Debt Securities Gross Unrealized Losses		(1,476)	(3,157)
Available For Sale Securities Debt Securities Fair Value		672,968	803,388
Available-for-sale Securities, Debt Securities		672,968	803,388
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		2,476,539	2,264,210
Available For Sale Securities Debt Securities Gross Unrealized Gain		104,030	111,841
Available For Sale Securities Debt Securities Gross Unrealized Losses		(4,848)	(2,084)
Available For Sale Securities Debt Securities Fair Value		2,575,721	2,373,967
Available-for-sale Securities, Debt Securities		2,575,721	2,373,967
Debt, State Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		602,995	674,022
Available For Sale Securities Debt Securities Gross Unrealized Gain		28,828	37,615
Available For Sale Securities Debt Securities Gross Unrealized Losses		(4,511)	(787)
Available For Sale Securities Debt Securities Fair Value		627,312	710,850
Available-for-sale Securities, Debt Securities		627,312	710,850
Revenue Subject to Refund [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		442,026	504,778
Available For Sale Securities Debt Securities Gross Unrealized Gain		34,132	35,619
Available For Sale Securities Debt Securities Gross Unrealized Losses		0	(289)
Available For Sale Securities Debt Securities Fair Value		476,158	540,108
Available-for-sale Securities, Debt Securities		476,158	540,108
Corporation [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		385,972	413,234
Available For Sale Securities Debt Securities Gross Unrealized Gain		13,156	18,976
Available For Sale Securities Debt Securities Gross Unrealized Losses		(709)	(855)
Available For Sale Securities Debt Securities Fair Value		398,419	431,355
Available-for-sale Securities, Debt Securities		398,419	431,355
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		5,055,909	5,036,958
Available For Sale Securities Debt Securities Gross Unrealized Gain		144,787	187,960
Available For Sale Securities Debt Securities Gross Unrealized Losses		(42,485)	(24,781)
Available For Sale Securities Debt Securities Fair Value		5,158,211	5,200,137
Available-for-sale Securities, Debt Securities		5,158,211	5,200,137
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,105,906	1,276,403
Available For Sale Securities Debt Securities Gross Unrealized Gain		28,837	28,734
Available For Sale Securities Debt Securities Gross Unrealized Losses		(7,119)	(9,501)
Available For Sale Securities Debt Securities Fair Value		1,127,624	1,295,636
Available-for-sale Securities, Debt Securities		1,127,624	1,295,636
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,634,056	2,019,032
Available For Sale Securities Debt Securities Gross Unrealized Gain		17,722	18,868
Available For Sale Securities Debt Securities Gross Unrealized Losses		(11,681)	(11,974)
Available For Sale Securities Debt Securities Fair Value		1,640,097	2,025,926
Available-for-sale Securities, Debt Securities		1,640,097	2,025,926
Industrial Property [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,888,762	1,606,724
Available For Sale Securities Debt Securities Gross Unrealized Gain		80,342	117,206
Available For Sale Securities Debt Securities Gross Unrealized Losses		(17,257)	(5,131)
Available For Sale Securities Debt Securities Fair Value		1,951,847	1,718,799
Available-for-sale Securities, Debt Securities		1,951,847	1,718,799
Domestic Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		1,264,970	1,140,801
Available For Sale Securities Debt Securities Gross Unrealized Gain		35,728	38,080
Available For Sale Securities Debt Securities Gross Unrealized Losses		(11,980)	(7,673)
Available For Sale Securities Debt Securities Fair Value		1,288,718	1,171,208
Available-for-sale Securities, Debt Securities		1,288,718	1,171,208
Public Utility, Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		187,325	184,107
Available For Sale Securities Debt Securities Gross Unrealized Gain		10,549	12,436
Available For Sale Securities Debt Securities Gross Unrealized Losses		(1,549)	(1)
Available For Sale Securities Debt Securities Fair Value		196,325	196,542
Available-for-sale Securities, Debt Securities		196,325	196,542
Other Security Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis		80,796	86,294
Available For Sale Securities Debt Securities Gross Unrealized Gain		446	1,370
Available For Sale Securities Debt Securities Gross Unrealized Losses		(18)	(2)
Available For Sale Securities Debt Securities Fair Value		81,224	87,662
Available-for-sale Securities, Debt Securities		81,224	87,662
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment		76,065	72,901
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		(15,824)	(17,501)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		0	0
Held-to-maturity Securities, Fair Value		91,889	90,402
Held-to-maturity Securities		76,065	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		20,025	23,278
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		(2,637)	(2,854)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		0	0
Held-to-maturity Securities, Fair Value		22,662	26,132
Held-to-maturity Securities		20,025	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		5,000	4,998
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		(65)	(291)
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss		0	0
Held-to-maturity Securities, Fair Value		5,065	5,289
Held-to-maturity Securities		$ 5,000	$ 4,998

[1] Gross unrealized losses for residential mortgage-backed securities include $1,023,313 and $1,095,671 as of September 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.