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Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Jun. 30, 2022 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Mar. 31, 2022
Variable Interest Entity [Line Items] |  |  |  |  |
Cash funding used to purchase Markel CATCo Funds' interests in Markel CATCo Re |  |  |  |  | $ 45,100
Additional payments made, net of insurance proceeds, to investors by Markel |  |  |  |  | $ 101,900
Returned capital from Markel CATCo Re | $ 24,900 |  |  |  |
Investment in Markel CATCo Re |  | $ 20,100 | $ 20,100 |  |
Percentage of Markel CATCo Re net equity by the Company |  | 52.00% | 23.00% |  |
Prior Year Claims and Claims Adjustment Expense |  | $ 455,300 | $ 38,600 | $ 167,400 |
Tail risk cover in proposed CATCo transaction |  | 95,000 |  |  |
Noncontrolling Interests [Member] |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Redemption of Markel CATCo Re noncontrolling interests |  | (117,227) | (62,646) | (22,261) |
Market CATCo Re |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | $ (58,100) | $ (71,500) | $ (89,900) |

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