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Investments (Summary Of Net Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Gain (Loss) on Securities [Line Items] |  |  |  |
Net realized investment gains (losses) | $ 13,891 | $ (36,093) | $ (4,604) | $ (38,159)
Change in fair value of securities sold during the period | (6,652) | 2,683 | (11,263) | 16,706
Change in fair value of securities held at the end of the period | 910,291 | (232,507) | 1,705,661 | 612,626
Total change in fair value of equity securities | 903,639 | (229,824) | 1,694,398 | 629,332
Net investment gains (losses) | 917,530 | (265,917) | 1,689,794 | 591,173
Change in net unrealized losses on available-for-sale investments included in other comprehensive income (loss): | 551,244 | (208,405) | 358,877 | (170,606)
Fixed Maturity Securities [Member] |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |
Change in net unrealized losses on available-for-sale investments included in other comprehensive income (loss): | 546,386 | (208,598) | 361,659 | (167,411)
Short-term investments [Member] |  |  |  |
Gain (Loss) on Securities [Line Items] |  |  |  |
Change in net unrealized losses on available-for-sale investments included in other comprehensive income (loss): | $ 4,858 | $ 193 | $ (2,782) | $ (3,195)

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