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Investments - Accrued Investment Income (Details) - USD ($) $ in Thousands | Mar. 31, 2024 | Dec. 31, 2023
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Accrued Interest on Investments [Line Items] |  |
Accrued investment income | $ 68,034 | $ 66,339
Available-for-Sale Securities |  |
Accrued Interest on Investments [Line Items] |  |
Accrued investment income | $ 66,300 | $ 64,600

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