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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
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Disaggregation of Revenue [Line Items] |  |
Leasing revenues | $ 40,753 | $ 41,752
Program services and other fronting fees | 36,030 | 28,890
Equity method and other investments income (loss) | 26,025 | (885)
Other revenues (losses) | 719 | 8,341
Products Revenues and Services and Other Revenues | 1,218,478 | 1,143,787
Markel Ventures [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Leasing revenues | 40,753 | 41,752
Program services and other fronting fees | 0 | 0
Equity method and other investments income (loss) | 5,179 | 1,495
Other revenues (losses) | 727 | 8,316
Products Revenues and Services and Other Revenues | 1,139,541 | 1,103,939
Other Insurance Operations [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Leasing revenues | 0 | 0
Program services and other fronting fees | 36,030 | 28,890
Equity method and other investments income (loss) | 20,846 | (2,380)
Other revenues (losses) | (8) | 25
Products Revenues and Services and Other Revenues | 78,937 | 39,848
Revenue from contracts with customers [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 1,114,951 | 1,065,689
Revenue from contracts with customers [Member] | Products [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 594,592 | 565,895
Revenue from contracts with customers [Member] | Services [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 500,423 | 489,335
Revenue from contracts with customers [Member] | Investment management [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 19,936 | 10,459
Revenue from contracts with customers [Member] | Markel Ventures [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 1,092,882 | 1,052,376
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Products [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 594,592 | 565,895
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Services [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 498,290 | 486,481
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Investment management [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 0 | 0
Revenue from contracts with customers [Member] | Other Insurance Operations [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 22,069 | 13,313
Revenue from contracts with customers [Member] | Other Insurance Operations [Member] | Products [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 0 | 0
Revenue from contracts with customers [Member] | Other Insurance Operations [Member] | Services [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | 2,133 | 2,854
Revenue from contracts with customers [Member] | Other Insurance Operations [Member] | Investment management [Member] |  |
Disaggregation of Revenue [Line Items] |  |
Other revenues | $ 19,936 | $ 10,459

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