v3.25.1
Products, Services and Other Revenues (Schedule Of Revenues From Contracts With Customers By Type) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Disaggregation of Revenue [Line Items]    
Leasing revenues $ 53,648 $ 40,753
Fronting fees 39,654 36,030
Equity method and other investments income (loss) 36,400 26,025
Other revenues (losses) 1,270 719
Products Revenues and Services and Other Revenues 1,221,707 1,218,478
Markel Ventures [Member]    
Disaggregation of Revenue [Line Items]    
Leasing revenues 53,648 40,753
Fronting fees 0 0
Equity method and other investments income (loss) 10,551 5,179
Other revenues (losses) 1,227 727
Products Revenues and Services and Other Revenues 1,127,878 1,139,541
Other [Member]    
Disaggregation of Revenue [Line Items]    
Leasing revenues 0 0
Fronting fees 39,654 36,030
Equity method and other investments income (loss) 25,849 20,846
Other revenues (losses) 43 (8)
Products Revenues and Services and Other Revenues 93,829 78,937
Revenue from contracts with customers [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 1,090,735 1,114,951
Revenue from contracts with customers [Member] | Products [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 554,117 594,592
Revenue from contracts with customers [Member] | Services [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 510,750 500,423
Revenue from contracts with customers [Member] | Management Fees [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 25,868 19,936
Revenue from contracts with customers [Member] | Markel Ventures [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 1,062,452 1,092,882
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Products [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 554,117 594,592
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Services [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 508,335 498,290
Revenue from contracts with customers [Member] | Markel Ventures [Member] | Management Fees [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 0 0
Revenue from contracts with customers [Member] | Other [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 28,283 22,069
Revenue from contracts with customers [Member] | Other [Member] | Products [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 0 0
Revenue from contracts with customers [Member] | Other [Member] | Services [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues 2,415 2,133
Revenue from contracts with customers [Member] | Other [Member] | Management Fees [Member]    
Disaggregation of Revenue [Line Items]    
Other revenues $ 25,868 $ 19,936