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Goodwill And Intangible Assets (Components Of Goodwill) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023
Goodwill [Line Items] |  |  |  |
Goodwill, beginning balance |  | $ 2,624,749 | [1] | $ 2,638,838
Goodwill, Acquired During Period |  | 114,589 |  |
Goodwill, Adjustments to preliminary purchase price allocation |  |  |  | (16,752)
Foreign currency movements and other adjustments |  | (3,471) |  | 2,663
Goodwill, ending balance | [1] | 2,735,867 |  | 2,624,749
Accumulated impairment losses | [1] | 190,600 |  | 190,600
Insurance [Member] |  |  |  |
Goodwill [Line Items] |  |  |  |
Goodwill, beginning balance |  | 772,823 | [1] | 771,628
Goodwill, Acquired During Period |  | 0 |  |
Goodwill, Adjustments to preliminary purchase price allocation |  |  |  | 0
Foreign currency movements and other adjustments |  | (3,247) |  | 1,195
Goodwill, ending balance | [1] | 769,576 |  | 772,823
Reinsurance [Member] |  |  |  |
Goodwill [Line Items] |  |  |  |
Goodwill, beginning balance |  | 122,745 | [1] | 122,745
Goodwill, Acquired During Period |  | 0 |  |
Goodwill, Adjustments to preliminary purchase price allocation |  |  |  | 0
Foreign currency movements and other adjustments |  | 0 |  | 0
Goodwill, ending balance | [1] | 122,745 |  | 122,745
Markel Ventures [Member] |  |  |  |
Goodwill [Line Items] |  |  |  |
Goodwill, beginning balance |  | 1,137,654 | [1] | 1,153,909
Goodwill, Acquired During Period |  | 114,589 |  |
Goodwill, Adjustments to preliminary purchase price allocation |  |  |  | (16,752)
Foreign currency movements and other adjustments |  | (434) |  | 497
Goodwill, ending balance | [1] | 1,251,809 |  | 1,137,654
Accumulated impairment losses | [1] | 18,700 |  | 18,700
Other Insurance Operations |  |  |  |
Goodwill [Line Items] |  |  |  |
Goodwill, beginning balance | [2] | 591,527 | [1] | 590,556
Goodwill, Acquired During Period | [2] | 0 |  |
Goodwill, Adjustments to preliminary purchase price allocation | [2] |  |  | 0
Foreign currency movements and other adjustments | [2] | 210 |  | 971
Goodwill, ending balance | [1],[2] | 591,737 |  | 591,527
Accumulated impairment losses | [1] | $ 171,900 |  | $ 171,900
[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.
[2] | Amounts included in other insurance operations reflect the Company's operations that are not included in a reportable segment and are primarily related to the Company's program services and insurance-linked securities operations.

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