Investments in Fixed Maturity Securities (Investments in Fixed Maturity Securities) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total held to maturity, Amortized Cost	$ 101,320,000		$ 102,951,000
Total held to maturity, Gross Unrealized Gains	14,900,000		24,420,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	116,220,000		127,371,000
Total held to maturity, Carrying Value	101,320,000		102,951,000
Total available for sale, Amortized Cost	11,190,311,000		11,115,003,000
Total available for sale, Gross Unrealized Gains	436,347,000		758,662,000
Total available for sale, Gross Unrealized Losses	(111,134,000)		(32,660,000)
Total available for sale, Fair Value	11,515,524,000		11,841,005,000
Total available for sale, Carrying Value	11,515,524,000		11,841,005,000
Total investment in fixed maturity securities, Amortized Cost	11,291,631,000		11,217,954,000
Total investments in fixed maturity securities, Gross Unrealized Gains	451,247,000		783,082,000
Total investments in fixed maturity securities, Gross Unrealized Losses	(111,134,000)		(32,660,000)
Total investments in fixed maturity securities, Fair Value	11,631,744,000		11,968,376,000
Total investments in fixed maturity securities, carrying value	11,616,844,000		11,943,956,000
U.S. government and government agency
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	858,319,000		827,591,000
Total available for sale, Gross Unrealized Gains	34,522,000		72,532,000
Total available for sale, Gross Unrealized Losses	(7,982,000)		(1,660,000)
Total available for sale, Fair Value	884,859,000		898,463,000
Total available for sale, Carrying Value	884,859,000		898,463,000
State and municipal
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	4,085,791,000		4,449,238,000
Total available for sale, Gross Unrealized Gains	162,330,000		328,974,000
Total available for sale, Gross Unrealized Losses	(29,837,000)		(9,693,000)
Total available for sale, Fair Value	4,218,284,000		4,768,519,000
Total available for sale, Carrying Value	4,218,284,000		4,768,519,000
Residential mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	1,248,693,000	[1]	1,395,739,000	[1]
Total available for sale, Gross Unrealized Gains	25,895,000	[1]	53,846,000	[1]
Total available for sale, Gross Unrealized Losses	(25,941,000)	[1]	(7,456,000)	[1]
Total available for sale, Fair Value	1,248,647,000	[1]	1,442,129,000	[1]
Total available for sale, Carrying Value	1,248,647,000	[1]	1,442,129,000	[1]
Non-credit portion of other-than-temporary impairments ("OTTI")	1,961,247		3,037,000
Commercial
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	76,454,000		268,671,000
Total available for sale, Gross Unrealized Gains	5,670,000		5,641,000
Total available for sale, Gross Unrealized Losses	(988,000)		(744,000)
Total available for sale, Fair Value	81,136,000		273,568,000
Total available for sale, Carrying Value	81,136,000		273,568,000
Corporate
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	4,076,585,000		3,378,884,000
Total available for sale, Gross Unrealized Gains	156,256,000		235,289,000
Total available for sale, Gross Unrealized Losses	(30,100,000)		(12,525,000)
Total available for sale, Fair Value	4,202,741,000		3,601,648,000
Total available for sale, Carrying Value	4,202,741,000		3,601,648,000
Foreign government
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total available for sale, Amortized Cost	844,469,000		794,880,000
Total available for sale, Gross Unrealized Gains	51,674,000		62,380,000
Total available for sale, Gross Unrealized Losses	(16,286,000)		(582,000)
Total available for sale, Fair Value	879,857,000		856,678,000
Total available for sale, Carrying Value	879,857,000		856,678,000
State and municipal
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total held to maturity, Amortized Cost	68,929,000		65,190,000
Total held to maturity, Gross Unrealized Gains	11,172,000		18,529,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	80,101,000		83,719,000
Total held to maturity, Carrying Value	68,929,000		65,190,000
Residential mortgage-backed securities
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total held to maturity, Amortized Cost	27,393,000		32,764,000
Total held to maturity, Gross Unrealized Gains	3,311,000		5,286,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	30,704,000		38,050,000
Total held to maturity, Carrying Value	27,393,000		32,764,000
Corporate
Schedule of Available-for-sale and Held-to-maturity Securities [Table] [Line Items]
Total held to maturity, Amortized Cost	4,998,000		4,997,000
Total held to maturity, Gross Unrealized Gains	417,000		605,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	5,415,000		5,602,000
Total held to maturity, Carrying Value	$ 4,998,000		$ 4,997,000

[1] Gross unrealized losses for mortgage-backed securities include $1,961,247 and $3,037,000, as of December 31, 2013 and 2012, respectively, related to the non-credit portion of OTTI recognized in other comprehensive income.