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Products, Services and Other Revenues (Schedule Of Revenues From Contracts With Customers By Type) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Disaggregation of Revenue [Line Items] |  |  |
Leasing revenues | $ 176,293 | $ 188,904 | $ 157,552
Fronting fees | 187,480 | 154,838 | 147,612
Equity method and other investments income (loss) | 58,830 | (13,598) | (15,120)
Disposition gains | 0 | 16,923 | 225,828
Other | 7,211 | 42,733 | 33,970
Total products revenues and services and other revenues | 5,460,636 | 5,249,565 | 5,236,521
Markel Ventures [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Leasing revenues | 176,293 | 188,904 | 157,552
Fronting fees | 0 | 0 | 0
Equity method and other investments income (loss) | 6,577 | (1,744) | 2,541
Disposition gains | 0 | 0 | 0
Other | 6,805 | 42,693 | 32,930
Total products revenues and services and other revenues | 5,113,078 | 4,979,768 | 4,756,618
Other [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Leasing revenues | 0 | 0 | 0
Fronting fees | 187,480 | 154,838 | 147,612
Equity method and other investments income (loss) | 52,253 | (11,854) | (17,661)
Disposition gains | 0 | 16,923 | 225,828
Other | 406 | 40 | 1,040
Total products revenues and services and other revenues | 347,558 | 269,797 | 479,903
Revenue from Contract with Customer [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 5,030,822 | 4,859,765 | 4,686,679
Revenue from Contract with Customer [Member] | Products [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 2,607,581 | 2,487,054 | 2,379,399
Revenue from Contract with Customer [Member] | Services [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 2,326,015 | 2,273,202 | 2,228,071
Revenue from Contract with Customer [Member] | Management Fees [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 97,226 | 99,509 | 79,209
Revenue from Contract with Customer [Member] | Markel Ventures [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 4,923,403 | 4,749,915 | 4,563,595
Revenue from Contract with Customer [Member] | Markel Ventures [Member] | Products [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 2,607,581 | 2,487,054 | 2,379,399
Revenue from Contract with Customer [Member] | Markel Ventures [Member] | Services [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 2,315,822 | 2,262,861 | 2,184,196
Revenue from Contract with Customer [Member] | Markel Ventures [Member] | Management Fees [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 0 | 0 | 0
Revenue from Contract with Customer [Member] | Other [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 107,419 | 109,850 | 123,084
Revenue from Contract with Customer [Member] | Other [Member] | Products [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 0 | 0 | 0
Revenue from Contract with Customer [Member] | Other [Member] | Services [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 10,193 | 10,341 | 43,875
Revenue from Contract with Customer [Member] | Other [Member] | Management Fees [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | $ 97,226 | $ 99,509 | $ 79,209

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