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Investments - Maturity Table (Details) - USD ($) $ in Thousands | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 454,603 | $ 182,325
Estimated Fair Value | 455,968 | $ 176,245
2020 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 77,265 |
Estimated Fair Value | 77,377 |
2021 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 103,336 |
Estimated Fair Value | 103,698 |
2022 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 34,997 |
Estimated Fair Value | 34,917 |
2038 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 260 |
Estimated Fair Value | 284 |
2039 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 2,880 |
Estimated Fair Value | 3,071 |
2042 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 7,558 |
Estimated Fair Value | 7,388 |
2043 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 12,274 |
Estimated Fair Value | 12,420 |
2044 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 18,838 |
Estimated Fair Value | 18,994 |
2045 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 20,227 |
Estimated Fair Value | 20,259 |
2046 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 32,152 |
Estimated Fair Value | 32,028 |
2047 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 48,145 |
Estimated Fair Value | 47,816 |
2048 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 13,205 |
Estimated Fair Value | 13,548 |
2049 |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 83,466 |
Estimated Fair Value | $ 84,168 |

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