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Investments - Maturity Table (Details) - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 2,013,021 | $ 485,756
Estimated Fair Value | 2,020,948 | $ 487,669
2020 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 416,977 |
Estimated Fair Value | 417,051 |
2021 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 354,463 |
Estimated Fair Value | 356,542 |
2022 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 814,700 |
Estimated Fair Value | 816,138 |
2023 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 22,696 |
Estimated Fair Value | 23,173 |
2038 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 173 |
Estimated Fair Value | 196 |
2039 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 2,301 |
Estimated Fair Value | 2,530 |
2042 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 6,922 |
Estimated Fair Value | 7,016 |
2043 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 10,804 |
Estimated Fair Value | 11,342 |
2044 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 14,552 |
Estimated Fair Value | 15,093 |
2045 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 13,909 |
Estimated Fair Value | 14,358 |
2046 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 22,838 |
Estimated Fair Value | 23,480 |
2047 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 34,843 |
Estimated Fair Value | 35,351 |
2048 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 8,824 |
Estimated Fair Value | 9,190 |
2049 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 67,357 |
Estimated Fair Value | 69,867 |
2050 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 145,958 |
Estimated Fair Value | 145,735 |
2054 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 75,704 |
Estimated Fair Value | $ 73,886 |

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