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Fair Value Measurements - Assets and Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Carrying Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Other invested assets | $ 3,100 | $ 3,100
FHLB Advance | 155,000 | 155,000
9% Convertible Junior Subordinated Debentures | 208,814 | 208,814
Total financial liabilities | 1,243,726 | 1,243,193
Fair Value | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Other invested assets | 3,100 | 3,100
FHLB Advance | 160,136 | 160,865
9% Convertible Junior Subordinated Debentures | 282,312 | 273,569
Total financial liabilities | $ 1,380,931 | 1,392,635
Senior Notes | 5.75% Senior Notes Due 2023 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Stated interest rate | 5.75% |
Senior Notes | 5.75% Senior Notes Due 2023 | Carrying Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Senior Notes | $ 240,762 | 240,597
Senior Notes | 5.75% Senior Notes Due 2023 | Fair Value | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Senior Notes | $ 261,248 | 261,752
Senior Notes | 5.25% Senior Notes Due 2028 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Stated interest rate | 5.25% |
Senior Notes | 5.25% Senior Notes Due 2028 | Carrying Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Senior Notes | $ 639,150 | 638,782
Senior Notes | 5.25% Senior Notes Due 2028 | Fair Value | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Senior Notes | $ 677,235 | $ 696,449
9% Convertible Junior Subordinated Debentures |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Stated interest rate | 9.00% |

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