Fair Value Measurements (Details) (USD $) | Jun. 30, 2014 | Dec. 31, 2013 |
In Thousands, unless otherwise specified |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | $4,614,479 | | $4,866,819 | |
Real estate acquired | 10,804 | [1] | 13,280 | [1] |
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 519,737 | | 683,015 | |
Real estate acquired | 0 | [1] | 0 | [1] |
Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 4,092,190 | | 4,181,060 | |
Real estate acquired | 0 | [1] | 0 | [1] |
Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 2,552 | | 2,744 | |
Real estate acquired | 10,804 | [1] | 13,280 | [1] |
U.S. Treasury securities and obligations of U.S. government corporations and agencies [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 474,818 | | 639,590 | |
U.S. Treasury securities and obligations of U.S. government corporations and agencies [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 474,818 | | 639,590 | |
U.S. Treasury securities and obligations of U.S. government corporations and agencies [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
U.S. Treasury securities and obligations of U.S. government corporations and agencies [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Obligations of U.S. states and political subdivisions [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 848,370 | | 921,367 | |
Obligations of U.S. states and political subdivisions [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Obligations of U.S. states and political subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 846,139 | | 918,944 | |
Obligations of U.S. states and political subdivisions [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 2,231 | | 2,423 | |
Corporate debt securities [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 2,195,771 | | 2,171,415 | |
Corporate debt securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Corporate debt securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 2,195,771 | | 2,171,415 | |
Corporate debt securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Asset-backed securities [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 368,806 | | 400,486 | |
Asset-backed securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Asset-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 368,806 | | 400,486 | |
Asset-backed securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Residential mortgage-backed securities [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 347,490 | | 358,537 | |
Residential mortgage-backed securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Residential mortgage-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 347,490 | | 358,537 | |
Residential mortgage-backed securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Commercial mortgage-backed securities [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 273,521 | | 271,383 | |
Commercial mortgage-backed securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Commercial mortgage-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 273,521 | | 271,383 | |
Commercial mortgage-backed securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Collateralized loan obligations [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 60,463 | | 60,295 | |
Collateralized loan obligations [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Collateralized loan obligations [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 60,463 | | 60,295 | |
Collateralized loan obligations [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Debt securities issued by foreign sovereign governments [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 42,229 | | 40,852 | |
Debt securities issued by foreign sovereign governments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 42,229 | | 40,852 | |
Debt securities issued by foreign sovereign governments [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Debt securities issued by foreign sovereign governments [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Total debt securities [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 4,611,468 | | 4,863,925 | |
Total debt securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 517,047 | | 680,442 | |
Total debt securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 4,092,190 | | 4,181,060 | |
Total debt securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 2,231 | | 2,423 | |
Equity securities [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 3,011 | | 2,894 | |
Equity securities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 2,690 | | 2,573 | |
Equity securities [Member] | Significant Other Observable Inputs (Level 2) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | 0 | | 0 | |
Equity securities [Member] | Significant Unobservable Inputs (Level 3) [Member] | ' | | ' | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | | ' | |
Total investments | $321 | | $321 | |
|
[1] | Real estate acquired through claim settlement, which is held for sale, is reported in Other Assets on the consolidated balance sheet. |