Investments (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010
Statutory Deposits
Carrying value of investments deposited with governmental authorities	$ 636,000,000	$ 574,000,000
Investments
Fixed maturities held to maturity, Amortized cost	1,187,591,000	1,189,801,000
Fixed maturities held to maturity, Fair value	1,248,501,000	1,240,678,000
Available for sale, Amortized cost	11,026,485,000	10,727,717,000
Available for sale, Gross unrealized gains	302,327,000	236,365,000
Available for sale, Gross unrealized losses	(79,417,000)	(141,746,000)
Available for sale, Fair value	11,249,395,000	10,822,336,000
Available for sale, OTTI	(114,206,000)	(114,206,000)
U.S. Government
Investments
Available for sale, Amortized cost	14,280,000	24,164,000
Available for sale, Gross unrealized gains	1,614,000	1,465,000
Available for sale, Gross unrealized losses		(3,000)
Available for sale, Fair value	15,894,000	25,626,000
U.S. Government agencies
Investments
Available for sale, Amortized cost	929,277,000	856,708,000
Available for sale, Gross unrealized gains	18,898,000	11,215,000
Available for sale, Gross unrealized losses	(1,299,000)	(3,324,000)
Available for sale, Fair value	946,876,000	864,599,000
States, municipalities and political subdivisions
Investments
Fixed maturities held to maturity, Amortized cost	1,187,591,000	1,189,801,000
Fixed maturities held to maturity, Gross unrealized gains	61,152,000	54,641,000
Fixed maturities held to maturity, Gross unrealized losses	(242,000)	(3,764,000)
Fixed maturities held to maturity, Fair value	1,248,501,000	1,240,678,000
Available for sale, Amortized cost	4,517,344,000	4,785,607,000
Available for sale, Gross unrealized gains	165,405,000	119,890,000
Available for sale, Gross unrealized losses	(26,486,000)	(63,858,000)
Available for sale, Fair value	4,656,263,000	4,841,639,000
Foreign governments
Investments
Available for sale, Amortized cost	710,883,000	790,710,000
Available for sale, Gross unrealized gains	12,914,000	11,248,000
Available for sale, Gross unrealized losses	(75,000)	(650,000)
Available for sale, Fair value	723,722,000	801,308,000
U.S. corporate
Investments
Available for sale, Amortized cost	2,299,514,000	1,944,114,000
Available for sale, Gross unrealized gains	43,561,000	34,544,000
Available for sale, Gross unrealized losses	(4,761,000)	(14,934,000)
Available for sale, Fair value	2,338,314,000	1,963,724,000
Available for sale, OTTI	(386,000)	(386,000)
Foreign corporate
Investments
Available for sale, Amortized cost	1,953,149,000	1,692,919,000
Available for sale, Gross unrealized gains	45,136,000	48,816,000
Available for sale, Gross unrealized losses	(7,836,000)	(10,107,000)
Available for sale, Fair value	1,990,449,000	1,731,628,000
Asset-backed: RMBS
Investments
Available for sale, Amortized cost	279,580,000	285,431,000
Available for sale, Gross unrealized gains	888,000	525,000
Available for sale, Gross unrealized losses	(33,794,000)	(41,416,000)
Available for sale, Fair value	246,674,000	244,540,000
Available for sale, OTTI	(113,820,000)	(113,820,000)
Asset-backed: CMBS
Investments
Available for sale, Amortized cost	238,933,000	248,258,000
Available for sale, Gross unrealized gains	12,285,000	7,850,000
Available for sale, Gross unrealized losses	(4,302,000)	(6,117,000)
Available for sale, Fair value	246,916,000	249,991,000
Other Asset Backed Securities
Investments
Available for sale, Amortized cost	83,525,000	99,806,000
Available for sale, Gross unrealized gains	1,626,000	812,000
Available for sale, Gross unrealized losses	(864,000)	(1,337,000)
Available for sale, Fair value	84,287,000	99,281,000
Equities
Investments
Gross unrealized gains on equities	67,300,000	92,500,000
Gross unrealized losses on equities	$ (13,800,000)	$ (4,500,000)

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