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Fair Value Measurements (Quantitative Disclosures of Fair Value Assets) (Details) (USD $) In Thousands | Jun. 30, 2011 | Dec. 31, 2010
--- | --- | ---
Fixed maturity securities, AFS | $ 2,525,237 |  | $ 2,342,742 |
Equity securities, AFS | 136,577 |  | 69,636 |
Short-term investments | 142,809 |  | 161,155 |
U.S. Government and Government Agencies [Member] | Fair Value [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 296,931 | [1] | 320,529 | [1]
Foreign Government [Member] | Fair Value [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 30,100 |  | 18,966 |
Obligations of States and Political Subdivisions [Member] | Fair Value [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 542,616 |  | 533,897 |
Corporate Securities [Member] | Fair Value [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 1,078,503 |  | 993,725 |
Asset-backed Securities ("ABS") [Member] | Fair Value [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 78,205 |  | 48,733 |
Commercial Mortgage-backed Securities ("CMBS") [Member] | Fair Value [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 109,124 |  | 104,475 |
Residential Mortgage Backed Securities ("RMBS") [Member] | Fair Value [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 389,758 |  | 322,417 |
Fair Value [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 2,525,237 |  | 2,342,742 |
Equity securities, AFS | 136,577 |  | 69,636 |
Short-term investments | 142,809 |  | 161,155 |
Receivable for proceeds related to sale of Selective HR Solutions ("Selective HR") | 4,531 |  | 5,002 |
Total financial assets measured on a recurring basis | 2,809,154 |  | 2,578,535 |
U.S. Government and Government Agencies [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 99,101 | [1] | 105,317 | [1]
Foreign Government [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Obligations of States and Political Subdivisions [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Corporate Securities [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Asset-backed Securities ("ABS") [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Commercial Mortgage-backed Securities ("CMBS") [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Residential Mortgage Backed Securities ("RMBS") [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 99,101 |  | 105,317 |
Equity securities, AFS | 136,577 |  | 69,636 |
Short-term investments | 142,809 |  | 161,155 |
Receivable for proceeds related to sale of Selective HR Solutions ("Selective HR") | 0 |  | 0 |
Total financial assets measured on a recurring basis | 378,487 |  | 336,108 |
U.S. Government and Government Agencies [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 197,830 | [1] | 215,212 | [1]
Foreign Government [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 30,100 |  | 18,966 |
Obligations of States and Political Subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 542,616 |  | 533,897 |
Corporate Securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 1,078,503 |  | 993,725 |
Asset-backed Securities ("ABS") [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 78,205 |  | 48,733 |
Commercial Mortgage-backed Securities ("CMBS") [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 108,683 |  | 104,290 |
Residential Mortgage Backed Securities ("RMBS") [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 389,758 |  | 322,417 |
Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 2,425,695 |  | 2,237,240 |
Equity securities, AFS | 0 |  | 0 |
Short-term investments | 0 |  | 0 |
Receivable for proceeds related to sale of Selective HR Solutions ("Selective HR") | 0 |  | 0 |
Total financial assets measured on a recurring basis | 2,425,695 |  | 2,237,240 |
U.S. Government and Government Agencies [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 | [1] | 0 | [1]
Foreign Government [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Obligations of States and Political Subdivisions [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Corporate Securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Asset-backed Securities ("ABS") [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Commercial Mortgage-backed Securities ("CMBS") [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 441 |  | 185 |
Residential Mortgage Backed Securities ("RMBS") [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 0 |  | 0 |
Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member] |  |  |  |
Fixed maturity securities, AFS | 441 |  | 185 |
Equity securities, AFS | 0 |  | 0 |
Short-term investments | 0 |  | 0 |
Receivable for proceeds related to sale of Selective HR Solutions ("Selective HR") | 4,531 |  | 5,002 |
Total financial assets measured on a recurring basis | $ 4,972 |  | $ 5,187 |
[1] | 1 U.S. government includes corporate securities fully guaranteed by the FDIC.

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