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Goodwill And Intangible Assets (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Goodwill And Intangible Assets [Line Items] |  |  |  |  |
Impairment of goodwill | $ 0 |  | $ 0 |  | $ 80,000
Impairment of intangible assets (excluding goodwill) | 0 |  | 0 |  | 0
Goodwill, carrying value | 2,735,867 | [1] | 2,624,749 | [1] | 2,638,838
Estimated amortization of intangible assets for 2025 | 172,700 |  |  |  |
Estimated amortization of intangible assets for 2026 | 165,500 |  |  |  |
Estimated amortization of intangible assets for 2027 | 154,900 |  |  |  |
Estimated amortization of intangible assets for 2028 | 146,100 |  |  |  |
Estimated amortization of intangible assets for 2029 | 142,000 |  |  |  |
Indefinite-lived intangible assets | $ 90,400 |  | $ 90,400 |  |
Nephila Holdings Limited [Member] |  |  |  |  |
Goodwill And Intangible Assets [Line Items] |  |  |  |  |
Impairment of goodwill |  |  |  |  | 80,000
Goodwill, carrying value |  |  |  |  | $ 221,800
[1] | As of December 31, 2024 and 2023, goodwill was net of accumulated impairment losses of $190.6 million, of which $171.9 million was in other insurance operations and $18.7 million was in Markel Ventures.

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