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Segment Reporting Disclosures (Summary of Additional Measures for Markel Ventures) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Segment Reporting Information [Line Items] |  |  |  |  |
Interest expense |  | $ 44,553 | $ 47,348 | $ 141,212 | $ 147,090
Income tax expense |  | 14,235 | 16,460 | 339,903 | (240,629)
Markel Ventures [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Depreciation expense |  | 26,857 | 23,738 | 81,639 | 75,304
Interest expense | [1] | 10,663 | 11,921 | 36,485 | 34,124
Income tax expense |  | 22,253 | 12,603 | 66,022 | 43,682
Capital expenditures |  | 65,616 | 48,294 | 135,159 | 144,974
Markel Ventures [Member] | Intercompany interest expense |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Interest expense | [1] | $ 6,600 | $ 6,600 | $ 19,900 | $ 20,700
[1] | Interest expense for the quarter and nine months ended September 30, 2023 included intercompany interest expense of $6.6 million and $19.9 million, respectively. Interest expense for the quarter and nine months ended September 30, 2022 included intercompany interest expense of $6.6 million and $20.7 million, respectively. Intercompany interest expense was eliminated in consolidation.

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