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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 | 6 Months Ended
--- | --- | ---
Jun. 30, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | $ 54,900 | $ 37,035 | $ 108,548 | $ 77,788
Fronting fees | 49,807 | 46,218 | 89,461 | 82,248
Equity method and other investments income (loss) | 24,740 | 10,764 | 61,140 | 36,789
Other revenues (losses) | 1,492 | 1,767 | 2,762 | 2,486
Products Revenues and Services and Other Revenues | 1,650,843 | 1,531,700 | 2,872,550 | 2,750,178
Markel Ventures [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | 54,900 | 37,035 | 108,548 | 77,788
Fronting fees | 0 | 0 | 0 | 0
Equity method and other investments income (loss) | 1,425 | 1,407 | 11,976 | 6,586
Other revenues (losses) | 1,609 | 1,777 | 2,836 | 2,504
Products Revenues and Services and Other Revenues | 1,546,403 | 1,451,174 | 2,674,281 | 2,590,715
Other [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Leasing revenues | 0 | 0 | 0 | 0
Fronting fees | 49,807 | 46,218 | 89,461 | 82,248
Equity method and other investments income (loss) | 23,315 | 9,357 | 49,164 | 30,203
Other revenues (losses) | (117) | (10) | (74) | (18)
Products Revenues and Services and Other Revenues | 104,440 | 80,526 | 198,269 | 159,463
Revenue from contracts with customers [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 1,519,904 | 1,435,916 | 2,610,639 | 2,550,867
Revenue from contracts with customers [Member] | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 839,681 | 840,636 | 1,393,798 | 1,435,228
Revenue from contracts with customers [Member] | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 650,641 | 572,734 | 1,161,391 | 1,073,157
Revenue from contracts with customers [Member] | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 29,582 | 22,546 | 55,450 | 42,482
Revenue from contracts with customers [Member] | Markel Ventures [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 1,488,469 | 1,410,955 | 2,550,921 | 2,503,837
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 839,681 | 840,636 | 1,393,798 | 1,435,228
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 648,788 | 570,319 | 1,157,123 | 1,068,609
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Other [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 31,435 | 24,961 | 59,718 | 47,030
Revenue from contracts with customers [Member] | Other [Member] | Products [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 0 | 0 | 0 | 0
Revenue from contracts with customers [Member] | Other [Member] | Services [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | 1,853 | 2,415 | 4,268 | 4,548
Revenue from contracts with customers [Member] | Other [Member] | Management Fees [Member] |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Other revenues | $ 29,582 | $ 22,546 | $ 55,450 | $ 42,482

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