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Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2022 | Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023 | Mar. 31, 2022
Variable Interest Entity [Line Items] |  |  |  |  |
Cash funding used to purchase Markel CATCo Funds' interests in Markel CATCo Re |  |  |  |  | $ 45,100
Returned capital from Markel CATCo Re | $ 24,900 |  |  |  |
Investment in Markel CATCo Re |  | $ 20,100 |  | $ 20,100 |
Percentage of Markel CATCo Re net equity held by the Company |  | 18.00% |  | 23.00% |
Tail risk cover in Markel CATCo transaction |  | $ 95,000 |  |  |
Favorable development on prior years' loss reserves |  | 77,023 | $ 71,317 |  |
Redemption of Markel CATCo Re noncontrolling interests |  | 0 | (88,997) |  |
Noncontrolling Interests [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Redemption of Markel CATCo Re noncontrolling interests |  |  | (62,646) |  |
Markel CATCo Re |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Favorable development on prior years' loss reserves |  | $ (15,700) | $ (44,800) |  |

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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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