Investments In Fixed Maturity Securities Investments in Fixed Maturity Securities (Investments in fixed maturity securities) (Details) - USD ($)		Mar. 31, 2017		Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		$ 88,947,000		$ 88,526,000
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		15,025,000		14,146,000
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		103,972,000		102,672,000
Total held to maturity, Carrying Value		88,947,000		88,526,000
Total available for sale, Amortized Cost		13,061,342,000		12,869,809,000
Total available for sale, Gross Unrealized Gains		341,982,000		326,916,000
Total available for sale, Gross Unrealized Losses		(69,292,000)		(94,583,000)
Total available for sale, Fair Value		13,334,032,000		13,102,142,000
Total available for sale, Carrying Value		13,334,032,000		13,102,142,000
Total investments in fixed maturity securities, Amortized Value		13,150,289,000		12,958,335,000
Total investments in fixed maturity securities, Gross Unrealized Gains		357,007,000		341,062,000
Total investments in fixed maturity securities, Gross Unrealized Losses		(69,292,000)		(94,583,000)
Total investments in fixed maturity securities, Fair Value		13,438,004,000		13,204,814,000
Total investments in fixed maturity securities, Carrying Value		$ 13,422,979,000		13,190,668,000
Minimum ownership of Common stockholders equity		10.00%
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		$ 864,556,000		858,773,000
Total available for sale, Gross Unrealized Gains		38,692,000		46,794,000
Total available for sale, Gross Unrealized Losses		(1,577,000)		(2,762,000)
Total available for sale, Fair Value		901,671,000		902,805,000
Total available for sale, Carrying Value		901,671,000		902,805,000
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		144,583,000		155,540,000
Total available for sale, Gross Unrealized Gains		347,000		304,000
Total available for sale, Gross Unrealized Losses		(2,126,000)		(2,981,000)
Total available for sale, Fair Value		142,804,000		152,863,000
Total available for sale, Carrying Value		142,804,000		152,863,000
U.S. government and government agency
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		472,112,000		496,187,000
Total available for sale, Gross Unrealized Gains		16,784,000		20,208,000
Total available for sale, Gross Unrealized Losses		(2,220,000)		(2,593,000)
Total available for sale, Fair Value		486,676,000		513,802,000
Total available for sale, Carrying Value		486,676,000		513,802,000
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		2,759,063,000		2,791,211,000
Total available for sale, Gross Unrealized Gains		69,226,000		58,559,000
Total available for sale, Gross Unrealized Losses		(15,887,000)		(26,315,000)
Total available for sale, Fair Value		2,812,402,000		2,823,455,000
Total available for sale, Carrying Value		2,812,402,000		2,823,455,000
Corporation [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		376,664,000		410,933,000
Total available for sale, Gross Unrealized Gains		8,290,000		6,172,000
Total available for sale, Gross Unrealized Losses		(5,639,000)		(6,452,000)
Total available for sale, Fair Value		379,315,000		410,653,000
Total available for sale, Carrying Value		379,315,000		410,653,000
Debt, State Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		504,312,000		524,682,000
Total available for sale, Gross Unrealized Gains		18,952,000		16,964,000
Total available for sale, Gross Unrealized Losses		(3,295,000)		(5,139,000)
Total available for sale, Fair Value		519,969,000		536,507,000
Total available for sale, Carrying Value		519,969,000		536,507,000
Revenue Subject to Refund [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		349,697,000		356,535,000
Total available for sale, Gross Unrealized Gains		20,013,000		19,181,000
Total available for sale, Gross Unrealized Losses		(146,000)		(165,000)
Total available for sale, Fair Value		369,564,000		375,551,000
Total available for sale, Carrying Value		369,564,000		375,551,000
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost	[1]	1,067,779,000		1,034,301,000
Total available for sale, Gross Unrealized Gains	[1]	14,081,000		15,431,000
Total available for sale, Gross Unrealized Losses	[1]	(13,030,000)		(12,950,000)
Total available for sale, Fair Value		1,068,830,000	[1]	1,036,782,000
Total available for sale, Carrying Value	[1]	1,068,830,000		1,036,782,000
Non-credit portion of other-than-temporary impairments (OTTI)		717,960		818,691
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		4,131,823,000		3,967,795,000
Total available for sale, Gross Unrealized Gains		127,263,000		121,650,000
Total available for sale, Gross Unrealized Losses		(14,290,000)		(20,918,000)
Total available for sale, Fair Value		4,244,796,000		4,068,527,000
Total available for sale, Carrying Value		4,244,796,000		4,068,527,000
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		4,350,677,000		4,443,383,000
Total available for sale, Gross Unrealized Gains		136,978,000		116,558,000
Total available for sale, Gross Unrealized Losses		(26,569,000)		(40,438,000)
Total available for sale, Fair Value		4,461,086,000		4,519,503,000
Total available for sale, Carrying Value		4,461,086,000		4,519,503,000
Debt, Local Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		360,941,000		360,022,000
Total available for sale, Gross Unrealized Gains		20,497,000		15,682,000
Total available for sale, Gross Unrealized Losses		(1,602,000)		(2,367,000)
Total available for sale, Fair Value		379,836,000		373,337,000
Total available for sale, Carrying Value		379,836,000		373,337,000
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		1,212,362,000		1,189,841,000
Total available for sale, Gross Unrealized Gains		14,428,000		15,735,000
Total available for sale, Gross Unrealized Losses		(15,156,000)		(15,931,000)
Total available for sale, Fair Value		1,211,634,000		1,189,645,000
Total available for sale, Carrying Value		1,211,634,000		1,189,645,000
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		2,029,812,000		1,913,830,000
Total available for sale, Gross Unrealized Gains		7,837,000		5,971,000
Total available for sale, Gross Unrealized Losses		(9,480,000)		(11,941,000)
Total available for sale, Fair Value		2,028,169,000		1,907,860,000
Total available for sale, Carrying Value		2,028,169,000		1,907,860,000
Industrial Property [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		2,391,507,000		2,315,567,000
Total available for sale, Gross Unrealized Gains		70,783,000		71,007,000
Total available for sale, Gross Unrealized Losses		(5,330,000)		(7,174,000)
Total available for sale, Fair Value		2,456,960,000		2,379,400,000
Total available for sale, Carrying Value		2,456,960,000		2,379,400,000
Domestic Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		1,445,707,000		1,369,001,000
Total available for sale, Gross Unrealized Gains		45,431,000		39,543,000
Total available for sale, Gross Unrealized Losses		(6,881,000)		(11,270,000)
Total available for sale, Fair Value		1,484,257,000		1,397,274,000
Total available for sale, Carrying Value		1,484,257,000		1,397,274,000
Public Utility, Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		238,801,000		229,154,000
Total available for sale, Gross Unrealized Gains		10,578,000		10,801,000
Total available for sale, Gross Unrealized Losses		(2,049,000)		(2,411,000)
Total available for sale, Fair Value		247,330,000		237,544,000
Total available for sale, Carrying Value		247,330,000		237,544,000
Other Security Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Total available for sale, Amortized Cost		55,808,000		54,073,000
Total available for sale, Gross Unrealized Gains		471,000		299,000
Total available for sale, Gross Unrealized Losses		(30,000)		(63,000)
Total available for sale, Fair Value		56,249,000		54,309,000
Total available for sale, Carrying Value		56,249,000		54,309,000
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		73,631,000		72,582,000
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		13,374,000		12,453,000
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		87,005,000		85,035,000
Total held to maturity, Carrying Value		73,631,000		72,582,000
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total held to maturity, Amortized Cost		15,316,000		15,944,000
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain		1,651,000		1,693,000
Held to Maturity Securities Accumulated Unrecognized Holding Loss		0		0
Total held to maturity, Fair Value		16,967,000		17,637,000
Total held to maturity, Carrying Value		$ 15,316,000		$ 15,944,000

[1] Gross unrealized losses for residential mortgage-backed securities include $717,960 and $818,691 as of March 31, 2017 and December 31, 2016, respectively, related to the non-credit portion of other-than-temporary impairments (“OTTI”) recognized in accumulated other comprehensive income.