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Products, Services and Other Revenues (Schedule Of Revenues From Contracts With Customers By Type) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | $ 60,156 | $ 45,726 | $ 168,704 | $ 123,514
Fronting fees | 70,073 | 47,613 | 159,534 | 129,861
Equity method and other investments income (loss) | 34,922 | 8,677 | 96,062 | 45,466
Other revenues (losses) | 6,610 | 1,501 | 9,372 | 3,987
Products Revenues and Services and Other Revenues | 1,483,101 | 1,348,149 | 4,355,651 | 4,098,327
Markel Insurance |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | 0 | 0 | 0 | 0
Fronting fees | 29,026 | 12,627 | 37,958 | 19,875
Equity method and other investments income (loss) | 12,373 | 2,798 | 10,515 | 9,143
Other revenues (losses) | 4,751 | 67 | 5,031 | 118
Products Revenues and Services and Other Revenues | 47,349 | 18,085 | 58,252 | 35,449
Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | 43,218 | 29,843 | 117,788 | 76,160
Fronting fees | 0 | 0 | 0 | 0
Equity method and other investments income (loss) | 0 | (86) | 350 | 658
Other revenues (losses) | 609 | 346 | 1,177 | 269
Products Revenues and Services and Other Revenues | 1,049,961 | 998,308 | 2,895,250 | 2,784,548
Financial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | 0 | 0 | 0 | 0
Fronting fees | 41,047 | 34,986 | 121,576 | 109,986
Equity method and other investments income (loss) | 1,528 | (5,989) | 46,701 | (3,004)
Other revenues (losses) | 0 | 0 | 0 | 0
Products Revenues and Services and Other Revenues | 73,356 | 54,503 | 255,227 | 175,798
Consumer and Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | 16,938 | 15,883 | 50,916 | 47,354
Fronting fees | 0 | 0 | 0 | 0
Equity method and other investments income (loss) | 0 | 0 | 0 | 0
Other revenues (losses) | 1,250 | 1,088 | 3,164 | 3,600
Products Revenues and Services and Other Revenues | 291,414 | 265,299 | 1,108,426 | 1,063,863
Corporate Operations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | 0 | 0 | 0 | 0
Fronting fees | 0 | 0 | 0 | 0
Equity method and other investments income (loss) | 21,021 | 11,954 | 38,496 | 38,669
Other revenues (losses) | 0 | 0 | 0 | 0
Products Revenues and Services and Other Revenues | 21,021 | 11,954 | 38,496 | 38,669
Revenue from contracts with customers [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 1,311,340 | 1,244,632 | 3,921,979 | 3,795,499
Revenue from contracts with customers [Member] | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 599,614 | 605,471 | 1,993,412 | 2,040,699
Revenue from contracts with customers [Member] | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 681,386 | 613,303 | 1,842,777 | 1,686,460
Revenue from contracts with customers [Member] | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 30,340 | 25,858 | 85,790 | 68,340
Revenue from contracts with customers [Member] | Markel Insurance |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 1,199 | 2,593 | 4,748 | 6,313
Revenue from contracts with customers [Member] | Markel Insurance | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Markel Insurance | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 1,199 | 2,593 | 4,748 | 6,313
Revenue from contracts with customers [Member] | Markel Insurance | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Industrial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 1,006,134 | 968,205 | 2,775,935 | 2,707,461
Revenue from contracts with customers [Member] | Industrial | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 417,986 | 432,120 | 1,197,798 | 1,261,664
Revenue from contracts with customers [Member] | Industrial | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 588,148 | 536,085 | 1,578,137 | 1,445,797
Revenue from contracts with customers [Member] | Industrial | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Financial |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 30,781 | 25,506 | 86,950 | 68,816
Revenue from contracts with customers [Member] | Financial | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Financial | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 441 | (352) | 1,160 | 476
Revenue from contracts with customers [Member] | Financial | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 30,340 | 25,858 | 85,790 | 68,340
Revenue from contracts with customers [Member] | Consumer and Other |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 273,226 | 248,328 | 1,054,346 | 1,012,909
Revenue from contracts with customers [Member] | Consumer and Other | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 181,628 | 173,351 | 795,614 | 779,035
Revenue from contracts with customers [Member] | Consumer and Other | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 91,598 | 74,977 | 258,732 | 233,874
Revenue from contracts with customers [Member] | Consumer and Other | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Corporate Operations |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Corporate Operations | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Corporate Operations | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Corporate Operations | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue from Contract with Customer | $ 0 | $ 0 | $ 0 | $ 0

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