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Investments (Net Investment Gains (Losses) and Change in Net Unrealized Gains On Available-For-Sale Investments) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Gain (Loss) on Securities [Line Items] |  |  |
Net realized investment gains (losses) | $ 4,423 | $ (42,177) | $ (40,983)
Change in fair value of equity securities sold during the period | (14,966) | 34,684 | (14,884)
Change in fair value of equity securities held at the end of the period | 1,817,762 | 1,531,547 | (1,539,866)
Change in fair value of equity securities | 1,802,796 | 1,566,231 | (1,554,750)
Net investment gains (losses) | 1,807,219 | 1,524,054 | (1,595,733)
Change in net unrealized gains on investments included in other comprehensive income (loss) | (165,423) | 390,558 | (1,463,876)
Fixed maturities [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Change in net unrealized gains on investments included in other comprehensive income (loss) | (152,630) | 389,498 | (1,474,890)
Short-term investments [Member] |  |  |
Gain (Loss) on Securities [Line Items] |  |  |
Change in net unrealized gains on investments included in other comprehensive income (loss) | $ (12,793) | $ 1,060 | $ 11,014

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