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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, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Disaggregation of Revenue [Line Items] |  |  |
Leasing revenues | $ 188,904 | $ 157,552 | $ 99,994
Program services and other fronting | 154,838 | 147,612 | 123,823
Equity method and other investments income (loss) | (13,598) | (15,120) | 13,317
Disposition gains | 16,923 | 225,828 | 0
Other | 42,733 | 33,970 | 33,727
Total products revenues and services and other revenues | 5,249,565 | 5,236,521 | 3,997,445
Markel Ventures [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Leasing revenues | 188,904 | 157,552 | 99,994
Program services and other fronting | 0 | 0 | 0
Equity method and other investments income (loss) | (1,744) | 2,541 | 6,133
Disposition gains | 0 | 0 | 0
Other | 42,693 | 32,930 | 32,212
Total products revenues and services and other revenues | 4,979,768 | 4,756,618 | 3,643,816
Other [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Leasing revenues | 0 | 0 | 0
Program services and other fronting | 154,838 | 147,612 | 123,823
Equity method and other investments income (loss) | (11,854) | (17,661) | 7,184
Disposition gains | 16,923 | 225,828 | 0
Other | 40 | 1,040 | 1,515
Total products revenues and services and other revenues | 269,797 | 479,903 | 353,629
Revenue from Contract with Customer [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 4,859,765 | 4,686,679 | 3,726,584
Revenue from Contract with Customer [Member] | Products [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 2,487,054 | 2,379,399 | 1,668,448
Revenue from Contract with Customer [Member] | Services [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 2,273,202 | 2,228,071 | 1,971,879
Revenue from Contract with Customer [Member] | Investment management [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 99,509 | 79,209 | 86,257
Revenue from Contract with Customer [Member] | Markel Ventures [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 4,749,915 | 4,563,595 | 3,505,477
Revenue from Contract with Customer [Member] | Markel Ventures [Member] | Products [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 2,487,054 | 2,379,399 | 1,668,448
Revenue from Contract with Customer [Member] | Markel Ventures [Member] | Services [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | 2,262,861 | 2,184,196 | 1,837,029
Revenue from Contract with Customer [Member] | Markel Ventures [Member] | Investment management [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 | 109,850 | 123,084 | 221,107
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 | 10,341 | 43,875 | 134,850
Revenue from Contract with Customer [Member] | Other [Member] | Investment management [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues from contracts with customers | $ 99,509 | $ 79,209 | $ 86,257

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