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Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2022 | Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023 | Dec. 31, 2023
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 |  | $ 20,100
Percentage of Markel CATCo Re net equity held by the Company |  | 16.00% |  | 16.00% |  | 23.00%
Favorable development on prior years' loss reserves |  |  |  | $ 221,298 | $ 139,208 |
Redemption of Markel CATCo Re noncontrolling interests |  |  |  | 0 | (88,997) |
Tail risk cover in Markel CATCo transaction |  | $ 95,000 |  | 95,000 |  |
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 |  | $ (8,400) | $ (8,700) | $ (24,100) | $ (53,500) |

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