Investments (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Investments
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ (127,000,000)		$ (127,000,000)		$ (118,600,000)
Net Investment Income
Gross investment income	103,900,000	104,900,000	204,000,000	205,000,000
Investment expenses	(2,300,000)	(2,300,000)	(4,600,000)	(5,000,000)
Net investment income	101,588,000	102,591,000	199,350,000	200,003,000
Net Realized Investment Gains (Losses)
Realized gains on investment portfolio	16,300,000	10,800,000	25,800,000	20,800,000
Realized losses on investment portfolio	(17,600,000)	(4,300,000)	(20,900,000)	(6,900,000)
Other-than-temporary impairment (OTTI):
Intent to sell	0	(800,000)	(300,000)	(3,500,000)
Credit component of OTTI securities	(1,800,000)	(10,800,000)	(6,400,000)	(12,700,000)
OTTI	(1,800,000)	(11,600,000)	(6,700,000)	(16,200,000)
Net realized investment gains (losses)	(3,156,000)	(5,090,000)	(1,840,000)	(2,284,000)
Roll Forward of Credit Losses in the Investment Portfolio
Balance, at the beginning of the period	51,300,000	29,200,000	46,700,000	27,300,000
Additions for credit losses on securities for which an OTTI was not previously recognized	400,000	9,100,000	2,500,000	10,500,000
Eliminations of securities issued by FG VIEs	0	(13,500,000)	0	(13,500,000)
Reductions for securities sold during the period	0	(5,000,000)	0	(5,000,000)
Additions for credit losses on securities for which an OTTI was previously recognized	1,400,000	1,700,000	3,900,000	2,200,000
Balance, at the end of the period	53,100,000	21,500,000	53,100,000	21,500,000
Fixed maturity securities
Net Investment Income
Gross investment income	102,800,000	103,100,000	201,700,000	201,600,000
Short-term investments.
Net Investment Income
Gross investment income	200,000	300,000	400,000	600,000
Assets Acquired in Refinancing Transactions
Net Investment Income
Gross investment income	900,000	1,500,000	1,900,000	2,800,000
Fixed, short-term maturity securities and assets acquired in refinancing transactions
Investments
Accrued investment income	$ 99,200,000		$ 99,200,000		$ 100,700,000