Investments In Fixed Maturity Securities Investments in Fixed Maturity Securities (Investments in fixed maturity securities) (Details) - USD ($)		Sep. 30, 2016		Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		$ 88,177,000		$ 96,267,000
Held to Maturity Securities Accumulated Unrecognized Holding Gain		19,620,000		(18,453,000)
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		107,797,000		114,720,000
Total held to maturity, Carrying Value		88,177,000		96,267,000
Total available for sale, Amortized Cost		13,019,875,000		12,012,041,000
Total available for sale, Gross Unrealized Gains		542,348,000		427,492,000
Total available for sale, Gross Unrealized Losses		(33,729,000)		(91,406,000)
Total available for sale, Fair Value		13,528,494,000		12,348,127,000
Total available for sale, Carrying Value		13,528,494,000		12,348,127,000
Total investments in fixed maturity securities, Amortized Value		13,108,052,000		12,108,308,000
Total investments in fixed maturity securities, Gross Unrealized Gains		561,968,000		445,945,000
Total investments in fixed maturity securities, Gross Unrealized Losses		(33,729,000)		(91,406,000)
Total investments in fixed maturity securities, Fair Value		13,636,291,000		12,462,847,000
Total investments in fixed maturity securities, Carrying Value		$ 13,616,671,000		12,444,394,000
Minimum ownership of Common stockholders equity		10.00%
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		$ 909,765,000		799,839,000
Total available for sale, Gross Unrealized Gains		58,477,000		50,310,000
Total available for sale, Gross Unrealized Losses		(2,490,000)		(12,689,000)
Total available for sale, Fair Value		965,752,000		837,460,000
Total available for sale, Carrying Value		965,752,000		837,460,000
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		108,928,000		64,975,000
Total available for sale, Gross Unrealized Gains		1,032,000		875,000
Total available for sale, Gross Unrealized Losses		(916,000)		(128,000)
Total available for sale, Fair Value		109,044,000		65,722,000
Total available for sale, Carrying Value		109,044,000		65,722,000
U.S. government and government agency
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		530,541,000		645,092,000
Total available for sale, Gross Unrealized Gains		25,383,000		27,660,000
Total available for sale, Gross Unrealized Losses		(931,000)		(2,333,000)
Total available for sale, Fair Value		554,993,000		670,419,000
Total available for sale, Carrying Value		554,993,000		670,419,000
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		2,707,492,000		2,510,816,000
Total available for sale, Gross Unrealized Gains		124,159,000		102,909,000
Total available for sale, Gross Unrealized Losses		(1,767,000)		(3,737,000)
Total available for sale, Fair Value		2,829,884,000		2,609,988,000
Total available for sale, Carrying Value		2,829,884,000		2,609,988,000
Corporation [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		374,355,000		388,904,000
Total available for sale, Gross Unrealized Gains		15,424,000		14,039,000
Total available for sale, Gross Unrealized Losses		(235,000)		(402,000)
Total available for sale, Fair Value		389,544,000		402,541,000
Total available for sale, Carrying Value		389,544,000		402,541,000
Debt, State Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		528,380,000		583,456,000
Total available for sale, Gross Unrealized Gains		33,688,000		28,068,000
Total available for sale, Gross Unrealized Losses		(560,000)		(2,070,000)
Total available for sale, Fair Value		561,508,000		609,454,000
Total available for sale, Carrying Value		561,508,000		609,454,000
Revenue Subject to Refund [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		366,360,000		439,772,000
Total available for sale, Gross Unrealized Gains		31,900,000		32,056,000
Total available for sale, Gross Unrealized Losses		(9,000)		(31,000)
Total available for sale, Fair Value		398,251,000		471,797,000
Total available for sale, Carrying Value		398,251,000		471,797,000
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost	[1]	1,131,545,000		1,126,382,000
Total available for sale, Gross Unrealized Gains	[1]	27,275,000		18,935,000
Total available for sale, Gross Unrealized Losses	[1]	(4,859,000)		(11,180,000)
Total available for sale, Fair Value		1,153,961,000	[1]	1,134,137,000
Total available for sale, Carrying Value	[1]	1,153,961,000		1,134,137,000
Non-credit portion of other-than-temporary impairments (OTTI)		857,252		1,269,491
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		3,746,954,000		3,403,953,000
Total available for sale, Gross Unrealized Gains		177,088,000		115,478,000
Total available for sale, Gross Unrealized Losses		(9,874,000)		(44,393,000)
Total available for sale, Fair Value		3,914,168,000		3,475,038,000
Total available for sale, Carrying Value		3,914,168,000		3,475,038,000
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		4,326,936,000		4,265,106,000
Total available for sale, Gross Unrealized Gains		237,364,000		201,342,000
Total available for sale, Gross Unrealized Losses		(2,585,000)		(6,269,000)
Total available for sale, Fair Value		4,561,715,000		4,460,179,000
Total available for sale, Carrying Value		4,561,715,000		4,460,179,000
Debt, Local Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		350,349,000		342,158,000
Total available for sale, Gross Unrealized Gains		32,193,000		24,270,000
Total available for sale, Gross Unrealized Losses		(14,000)		(29,000)
Total available for sale, Fair Value		382,528,000		366,399,000
Total available for sale, Carrying Value		382,528,000		366,399,000
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		1,240,473,000		1,191,357,000
Total available for sale, Gross Unrealized Gains		28,307,000		19,810,000
Total available for sale, Gross Unrealized Losses		(5,775,000)		(11,308,000)
Total available for sale, Fair Value		1,263,005,000		1,199,859,000
Total available for sale, Carrying Value		1,263,005,000		1,199,859,000
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		2,265,206,000		1,706,694,000
Total available for sale, Gross Unrealized Gains		15,729,000		12,892,000
Total available for sale, Gross Unrealized Losses		(12,074,000)		(14,414,000)
Total available for sale, Fair Value		2,268,861,000		1,705,172,000
Total available for sale, Carrying Value		2,268,861,000		1,705,172,000
Industrial Property [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		2,168,312,000		1,976,393,000
Total available for sale, Gross Unrealized Gains		111,260,000		75,168,000
Total available for sale, Gross Unrealized Losses		(3,692,000)		(30,027,000)
Total available for sale, Fair Value		2,275,880,000		2,021,534,000
Total available for sale, Carrying Value		2,275,880,000		2,021,534,000
Domestic Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		1,288,472,000		1,153,096,000
Total available for sale, Gross Unrealized Gains		52,419,000		31,744,000
Total available for sale, Gross Unrealized Losses		(5,384,000)		(11,819,000)
Total available for sale, Fair Value		1,335,507,000		1,173,021,000
Total available for sale, Carrying Value		1,335,507,000		1,173,021,000
Public Utility, Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		199,941,000		192,857,000
Total available for sale, Gross Unrealized Gains		11,593,000		8,321,000
Total available for sale, Gross Unrealized Losses		(785,000)		(2,527,000)
Total available for sale, Fair Value		210,749,000		198,651,000
Total available for sale, Carrying Value		210,749,000		198,651,000
Other Security Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		90,229,000		81,607,000
Total available for sale, Gross Unrealized Gains		1,816,000		245,000
Total available for sale, Gross Unrealized Losses		(13,000)		(20,000)
Total available for sale, Fair Value		92,032,000		81,832,000
Total available for sale, Carrying Value		92,032,000		81,832,000
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		71,608,000		77,129,000
Held to Maturity Securities Accumulated Unrecognized Holding Gain		17,388,000		(16,246,000)
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		88,996,000		93,375,000
Total held to maturity, Carrying Value		71,608,000		77,129,000
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		16,569,000		19,138,000
Held to Maturity Securities Accumulated Unrecognized Holding Gain		2,232,000		(2,207,000)
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		18,801,000		21,345,000
Total held to maturity, Carrying Value		$ 16,569,000		$ 19,138,000

[1] Gross unrealized losses for residential mortgage-backed securities include $857,252 and $1,269,491 as of September 30, 2016 and December 31, 2015, respectively, related to the non-credit portion of other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income.