v2.4.0.6
Investments - Schedule of Investments (Details) (USD $)
3 Months Ended 12 Months Ended
Mar. 31, 2012
Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]    
Fair Value $ 4,787,700,000 $ 4,773,400,000
Fair Value 429,600,000 397,300,000
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Due in One Year or Less 75,100,000  
Due after One Year to Five Years 505,700,000  
Due after Five Years to Ten Years 966,600,000  
Due after Ten Years 2,966,900,000  
Asset-backed Securities Not Due in a Single Maturity Date 273,400,000  
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 214,800,000 259,500,000
Less Than 12 Months, Unrealized Losses (8,000,000) (16,700,000)
12 Months or Longer, Fair Value 71,600,000 94,600,000
12 Months or Longer, Unrealized Losses (4,900,000) (6,600,000)
Available For Sale Securities, Continuous Unrealized Loss Position, Credit Losses Recognized Related to Securites in An Unrealized Loss Position, In a Position of 12 Months or Longer   0
Total, Fair Value 286,400,000 354,100,000
Total, Unrealized Losses (12,900,000) (23,300,000)
Available For Sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses Related to Securities that have Previously Recognized Foregin Currency Impairment 100,000 200,000
Available For Sale Securities, Continuous Unrealized Loss Position, Credit Losses Recognized Related to Securites in An Unrealized Loss Position 0  
Number of Issuers of Available for Sales Securities Continuous Unrealized Loss Possition Aggregate Losses Related to Securities that have Previously Recognized Foreign Currency impairment 1 1
Fixed Maturities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 4,297,600,000 4,266,100,000
Gross Unrealized Gains 499,600,000 518,400,000
Gross Unrealized Losses (9,500,000) (11,100,000)
Fair Value 4,787,700,000 4,773,400,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 190,400,000 173,500,000
Less Than 12 Months, Unrealized Losses (5,000,000) (5,200,000)
12 Months or Longer, Fair Value 66,300,000 89,500,000
12 Months or Longer, Unrealized Losses (4,500,000) (5,900,000)
Total, Fair Value 256,700,000 263,000,000
Total, Unrealized Losses (9,500,000) (11,100,000)
US Government and Government Agencies and Authorities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 429,100,000 439,400,000
Gross Unrealized Gains 45,900,000 52,300,000
Gross Unrealized Losses (600,000) 0
Fair Value 474,400,000 491,700,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 19,700,000 1,300,000
Less Than 12 Months, Unrealized Losses (600,000) 0
12 Months or Longer, Fair Value 0 0
12 Months or Longer, Unrealized Losses 0 0
Total, Fair Value 19,700,000 1,300,000
Total, Unrealized Losses (600,000) 0
Government National Mortgage Association Certificates and Obligations (GNMA) [Member]
   
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Asset-backed Securities Not Due in a Single Maturity Date 241,600,000  
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
   
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Asset-backed Securities Not Due in a Single Maturity Date 26,000,000  
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
   
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Asset-backed Securities Not Due in a Single Maturity Date 800,000  
Other Issuers [Member]
   
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Asset-backed Securities Not Due in a Single Maturity Date 5,000,000  
States and Political Subdivisions [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 1,666,600,000 1,705,000,000
Gross Unrealized Gains 159,300,000 148,400,000
Gross Unrealized Losses (500,000) (800,000)
Fair Value 1,825,400,000 1,852,600,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 0 2,000,000
Less Than 12 Months, Unrealized Losses 0 0
12 Months or Longer, Fair Value 12,300,000 12,000,000
12 Months or Longer, Unrealized Losses (500,000) (800,000)
Total, Fair Value 12,300,000 14,000,000
Total, Unrealized Losses (500,000) (800,000)
Bonds and Notes [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 2,120,400,000 2,040,100,000
Gross Unrealized Gains 288,600,000 311,600,000
Gross Unrealized Losses (7,500,000) (9,400,000)
Fair Value 2,401,500,000 2,342,300,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 170,200,000 169,600,000
Less Than 12 Months, Unrealized Losses (4,200,000) (5,100,000)
12 Months or Longer, Fair Value 51,300,000 74,700,000
12 Months or Longer, Unrealized Losses (3,300,000) (4,300,000)
Total, Fair Value 221,500,000 244,300,000
Total, Unrealized Losses (7,500,000) (9,400,000)
Redeemable Preferred Stocks [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 76,800,000 76,700,000
Gross Unrealized Gains 4,800,000 5,100,000
Gross Unrealized Losses (200,000) (100,000)
Fair Value 81,400,000 81,700,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 500,000 600,000
Less Than 12 Months, Unrealized Losses (200,000) (100,000)
12 Months or Longer, Fair Value 100,000 100,000
12 Months or Longer, Unrealized Losses 0 0
Total, Fair Value 600,000 700,000
Total, Unrealized Losses (200,000) (100,000)
Mortgage and Asset-backed [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 4,700,000 4,900,000
Gross Unrealized Gains 1,000,000 1,000,000
Gross Unrealized Losses (700,000) (800,000)
Fair Value 5,000,000 5,100,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 0 0
Less Than 12 Months, Unrealized Losses 0 0
12 Months or Longer, Fair Value 2,600,000 2,700,000
12 Months or Longer, Unrealized Losses (700,000) (800,000)
Total, Fair Value 2,600,000 2,700,000
Total, Unrealized Losses (700,000) (800,000)
Collateralized Debt Obligations [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Fair Value 2,900,000 2,900,000
Non-governmental Residential Mortgage-backed Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Fair Value 1,700,000 1,700,000
Other Asset Backed Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Fair Value 400,000 400,000
Commercial Mortgage Backed Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Fair Value   100,000
Equity Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 380,400,000 367,300,000
Gross Unrealized Gains 52,600,000 42,200,000
Gross Unrealized Losses (3,400,000) (12,200,000)
Fair Value 429,600,000 397,300,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 24,400,000 86,000,000
Less Than 12 Months, Unrealized Losses (3,000,000) (11,500,000)
12 Months or Longer, Fair Value 5,300,000 5,100,000
12 Months or Longer, Unrealized Losses (400,000) (700,000)
Total, Fair Value 29,700,000 91,100,000
Total, Unrealized Losses (3,400,000) (12,200,000)
Preferred Stock Finance, Insurance and Real Estate [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 94,400,000 94,400,000
Gross Unrealized Gains 3,300,000 1,000,000
Gross Unrealized Losses (300,000) (8,700,000)
Fair Value 97,400,000 86,700,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 0 54,900,000
Less Than 12 Months, Unrealized Losses 0 (8,100,000)
12 Months or Longer, Fair Value 2,400,000 2,200,000
12 Months or Longer, Unrealized Losses (300,000) (600,000)
Total, Fair Value 2,400,000 57,100,000
Total, Unrealized Losses (300,000) (8,700,000)
Preferred Stocks Other Industries [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 18,100,000 18,000,000
Gross Unrealized Gains 3,400,000 2,600,000
Gross Unrealized Losses (300,000) (100,000)
Fair Value 21,200,000 20,500,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 1,800,000 1,800,000
Less Than 12 Months, Unrealized Losses (200,000) 0
12 Months or Longer, Fair Value 2,800,000 2,800,000
12 Months or Longer, Unrealized Losses (100,000) (100,000)
Total, Fair Value 4,600,000 4,600,000
Total, Unrealized Losses (300,000) (100,000)
Common Stocks Manufacturing [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 65,300,000 64,600,000
Gross Unrealized Gains 21,900,000 18,900,000
Gross Unrealized Losses (100,000) (100,000)
Fair Value 87,100,000 83,400,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 1,200,000 1,500,000
Less Than 12 Months, Unrealized Losses (100,000) (100,000)
12 Months or Longer, Fair Value 0 100,000
12 Months or Longer, Unrealized Losses 0 0
Total, Fair Value 1,200,000 1,600,000
Total, Unrealized Losses (100,000) (100,000)
Common Stocks Other Industries [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 41,400,000 41,400,000
Gross Unrealized Gains 8,900,000 7,400,000
Gross Unrealized Losses (600,000) (1,800,000)
Fair Value 49,700,000 47,000,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 5,400,000 10,700,000
Less Than 12 Months, Unrealized Losses (600,000) (1,800,000)
12 Months or Longer, Fair Value 100,000 0
12 Months or Longer, Unrealized Losses 0 0
Total, Fair Value 5,500,000 10,700,000
Total, Unrealized Losses (600,000) (1,800,000)
Exchange Traded Funds [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 66,000,000 66,000,000
Gross Unrealized Gains 1,700,000 600,000
Gross Unrealized Losses 0 0
Fair Value 67,700,000 66,600,000
Limited Liability Companies and Limited Partnerships [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost Basis 95,200,000 82,900,000
Gross Unrealized Gains 13,400,000 11,700,000
Gross Unrealized Losses (2,100,000) (1,500,000)
Fair Value 106,500,000 93,100,000
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 16,000,000 17,100,000
Less Than 12 Months, Unrealized Losses (2,100,000) (1,500,000)
12 Months or Longer, Fair Value 0 0
12 Months or Longer, Unrealized Losses 0 0
Total, Fair Value 16,000,000 17,100,000
Total, Unrealized Losses (2,100,000) (1,500,000)
External Credit Rating, Investment Grade [Member] | Fixed Maturities [Member]
   
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Total, Unrealized Losses (6,500,000) (5,700,000)
External Credit Rating, Non Investment Grade [Member]
   
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Related to Securities that have Previously Recognized Foregin Currency Impairment (100,000) (200,000)
Percentage of Unrealized Loss Postion to Amortized Cost Basis of Available for Sale Security Average 3.00% 4.00%
External Credit Rating, Non Investment Grade [Member] | Fixed Maturities [Member]
   
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Total, Unrealized Losses $ (3,000,000) $ (5,400,000)