Investments - Estimated Fair Value of Investments in Fixed Maturities (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains	$ 284,200,000	$ 584,500,000
Available-for-sale Debt Securities, Gross Unrealized Loss Accumulated in Investments	79,700,000	8,100,000
Other Receivables	193,100,000	206,100,000
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	218,300,000
Investments in Fixed Maturities, Fair Value	4,575,000,000	4,860,200,000
Accrued Expenses and Other Liabilities	329,800,000	431,400,000
US Government and Government Agencies and Authorities [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains	22,800,000	45,100,000
Available-for-sale Debt Securities, Gross Unrealized Loss Accumulated in Investments	11,700,000	200,000
Investments in Fixed Maturities, Fair Value	362,200,000	428,900,000
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	155,900,000
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities [Line Items]
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	11,300,000
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Available-for-sale Securities [Line Items]
Asset-backed Securities Not Due at a Single Maturity Date, Fair Value	400,000
States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains	53,800,000	150,500,000
Available-for-sale Debt Securities, Gross Unrealized Loss Accumulated in Investments	20,200,000	100,000
Investments in Fixed Maturities, Fair Value	1,361,000,000	1,401,400,000
Corporate Bonds and Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains	205,000,000	385,400,000
Available-for-sale Debt Securities, Gross Unrealized Loss Accumulated in Investments	47,700,000	7,500,000
Investments in Fixed Maturities, Fair Value	2,793,700,000	2,993,400,000
Redeemable Preferred Stocks [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains	800,000	2,500,000
Available-for-sale Debt Securities, Gross Unrealized Loss Accumulated in Investments	0	0
Investments in Fixed Maturities, Fair Value	7,400,000	32,600,000
Mortgage and Asset Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Gains	1,800,000	1,000,000
Available-for-sale Debt Securities, Gross Unrealized Loss Accumulated in Investments	100,000	300,000
Investments in Fixed Maturities, Fair Value	50,700,000	3,900,000
Investments in Fixed Maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Other Receivables	2,500,000	0
Accrued Expenses and Other Liabilities	$ 0	$ 1,500,000