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Fair Value Measurements (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | $ 5,287,360 | $ 5,151,987
Equity securities, at fair value (cost 2019 - $4,016; 2018 - $3,993) | 4,057 | 3,932
Other | 205,444 | 96,403
Real estate acquired | 11,639 | 14,535
Total assets | 5,508,500 | 5,266,857
Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Other | 205,444 | 96,403
Real estate acquired | 0 | 0
Total assets | 251,980 | 142,599
Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Other | 0 | 0
Real estate acquired | 0 | 0
Total assets | 5,244,881 | 5,109,710
Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Other | 0 | 0
Real estate acquired | 11,639 | 14,535
Total assets | 11,639 | 14,548
Total fixed income securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 5,287,360 | 5,151,987
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 42,479 | 42,264
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 5,244,881 | 5,109,710
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 13
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 168,142 | 167,176
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 42,479 | 42,264
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 125,663 | 124,912
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 1,667,238 | 1,720,100
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 1,667,238 | 1,720,087
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 13
Corporate debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 2,456,069 | 2,400,762
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 2,456,069 | 2,400,762
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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Asset backed securities (“ABS”) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 218,481 | 112,033
Asset backed securities (“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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Asset backed securities (“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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 218,481 | 112,033
Asset backed securities (“ABS”) | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Residential mortgage backed securities (“RMBS”) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 180,485 | 178,961
Residential mortgage backed securities (“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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Residential mortgage backed securities (“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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 180,485 | 178,961
Residential mortgage backed securities (“RMBS”) | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Commercial mortgage backed securities (“CMBS”) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 269,283 | 267,660
Commercial mortgage backed securities (“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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Commercial mortgage backed securities (“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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 269,283 | 267,660
Commercial mortgage backed securities (“CMBS”) | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Collateralized loan obligations (“CLO”) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 327,662 | 305,295
Collateralized loan obligations (“CLO”) | 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, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Collateralized loan obligations (“CLO”) | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 327,662 | 305,295
Collateralized loan obligations (“CLO”) | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fixed income, available-for-sale, at fair value (amortized cost 2019 - $5,229,535; 2018 - $5,196,784) | 0 | 0
Equity securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost 2019 - $4,016; 2018 - $3,993) | 4,057 | 3,932
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 2019 - $4,016; 2018 - $3,993) | 4,057 | 3,932
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 2019 - $4,016; 2018 - $3,993) | 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 2019 - $4,016; 2018 - $3,993) | $ 0 | $ 0

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