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Fair Value Measurements (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | $ 6,661,596 | $ 5,737,892
Equity securities, at fair value (cost, 2020 - $17,522; 2019 - $17,188) | 18,215 | 17,328
Cash Equivalents | 288,941 | 164,693
Real estate acquired | 1,092 | 7,252
Total assets | 6,969,844 | 5,927,165
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash Equivalents | 275,668 | 164,693
Real estate acquired | 0 | 0
Total assets | 443,222 | 216,261
Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash Equivalents | 13,273 | 0
Real estate acquired | 0 | 0
Total assets | 6,525,530 | 5,703,652
Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash Equivalents | 0 | 0
Real estate acquired | 1,092 | 7,252
Total assets | 1,092 | 7,252
Total fixed income securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 6,661,596 | 5,737,892
Total fixed income securities | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 149,339 | 34,240
Total fixed income securities | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 6,512,257 | 5,703,652
Total fixed income securities | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
U.S. Treasury securities and obligations of U.S. government corporations and agencies |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 265,693 | 196,203
U.S. Treasury securities and obligations of U.S. government corporations and agencies | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 149,339 | 34,240
U.S. Treasury securities and obligations of U.S. government corporations and agencies | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 116,354 | 161,963
U.S. Treasury securities and obligations of U.S. government corporations and agencies | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
Obligations of U.S. states and political subdivisions |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 2,249,869 | 1,653,865
Obligations of U.S. states and political subdivisions | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
Obligations of U.S. states and political subdivisions | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 2,249,869 | 1,653,865
Obligations of U.S. states and political subdivisions | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
Corporate debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 2,844,288 | 2,785,122
Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
Corporate debt securities | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 2,844,288 | 2,785,122
Corporate debt securities | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
ABS |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 206,686 | 229,664
ABS | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
ABS | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 206,686 | 229,664
ABS | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
RMBS |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 431,166 | 268,586
RMBS | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
RMBS | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 431,166 | 268,586
RMBS | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
CMBS |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 327,502 | 278,986
CMBS | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
CMBS | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 327,502 | 278,986
CMBS | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
CLOs |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 310,490 | 325,466
CLOs | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
CLOs | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 310,490 | 325,466
CLOs | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 | 0
Debt securities issued by foreign sovereign governments |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 4,709 |
Debt securities issued by foreign sovereign governments | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 |
Debt securities issued by foreign sovereign governments | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 4,709 |
Debt securities issued by foreign sovereign governments | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 |
Other investments |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 21,193 |
Other investments | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 |
Other investments | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 21,193 |
Other investments | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale | 0 |
Equity securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost, 2020 - $17,522; 2019 - $17,188) | 18,215 | 17,328
Equity securities | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost, 2020 - $17,522; 2019 - $17,188) | 18,215 | 17,328
Equity securities | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost, 2020 - $17,522; 2019 - $17,188) | 0 | 0
Equity securities | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost, 2020 - $17,522; 2019 - $17,188) | $ 0 | $ 0

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