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Investments - Maturity Table (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 2,081,236 | $ 485,756
Estimated Fair Value | 2,090,707 | $ 487,669
2020 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 214,950 |
Estimated Fair Value | 214,970 |
2021 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 454,287 |
Estimated Fair Value | 455,932 |
2022 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 878,920 |
Estimated Fair Value | 880,483 |
2023 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 139,699 |
Estimated Fair Value | 140,147 |
2038 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 172 |
Estimated Fair Value | 195 |
2039 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 2,058 |
Estimated Fair Value | 2,271 |
2042 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 5,738 |
Estimated Fair Value | 5,750 |
2043 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 9,572 |
Estimated Fair Value | 10,027 |
2044 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 12,993 |
Estimated Fair Value | 13,540 |
2045 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 12,176 |
Estimated Fair Value | 12,611 |
2046 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 19,044 |
Estimated Fair Value | 19,485 |
2047 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 28,940 |
Estimated Fair Value | 29,448 |
2048 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 6,907 |
Estimated Fair Value | 7,209 |
2049 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 56,060 |
Estimated Fair Value | 58,279 |
2050 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 167,454 |
Estimated Fair Value | 168,041 |
2054 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 72,266 |
Estimated Fair Value | $ 72,319 |

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