v3.25.2
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