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Investments, Change in Realized and Unrealized Gains and Losses (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2023 | Sep. 30, 2023
Gain (Loss) on Securities [Line Items] |  |
Change in net realized and unrealized investment losses | $ 18,800 | $ 100,000

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