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Fair Value Measurements - Liabilities Not Measured at Fair Value (Details) - USD ($) $ in Thousands | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
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% |
9% Debentures |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Stated interest rate | 9.00% |
Carrying Value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
FHLB Advance | $ 155,000 | $ 155,000
5.75% Notes | 418,848 | 418,560
9% Debentures | 256,872 | 256,872
Total financial liabilities | 830,720 | 830,432
Fair Value | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
FHLB Advance | 149,756 | 152,124
5.75% Notes | 446,730 | 465,473
9% Debentures | 350,897 | 353,507
Total financial liabilities | $ 947,383 | $ 971,104

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