v3.25.2
Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Segment Reporting Information [Line Items]        
Earned premiums $ 2,141,691 $ 2,077,099 $ 4,231,065 $ 4,204,726
Net investment income 230,009 223,061 467,104 441,330
Net investment gains (losses) 580,223 (130,017) 431,152 772,264
Products revenues 846,925 847,219 1,408,049 1,448,059
Services and other revenues 803,918 684,481 1,464,501 1,302,119
Operating revenues 4,602,766 3,701,843 8,001,871 8,168,498
Attritional Current Year Claims and Claims Adjustment Expense (1,371,953) (1,376,850) (2,710,661) (2,741,620)
Catastrophe Current Year Claims and Claims Adjustment Expense 5,187 0 (60,877) 0
Losses and loss adjustment expenses, prior accident year 78,732 144,275 228,839 221,298
Amortization of policy acquisition costs (435,365) (421,639) (852,387) (856,226)
Other underwriting expenses (338,846) (288,656) (669,262) (592,821)
Products expenses (707,381) (693,693) (1,207,289) (1,216,940)
Services and other expenses (674,587) (611,063) (1,242,215) (1,147,901)
Amortization of acquired intangible assets (51,213) (44,237) (98,155) (88,522)
Operating Income 1,107,340 409,980 1,389,864 1,745,766
Interest expense (53,076) (52,597) (105,216) (98,145)
Net foreign exchange gains (losses) (191,909) 8,711 (264,542) 60,211
Income before income taxes 862,355 366,094 1,020,106 1,707,832
Markel Insurance        
Segment Reporting Information [Line Items]        
Earned premiums 2,063,622 2,004,166 4,080,161 4,050,645
Net investment income 0 0 0 0
Net investment gains (losses) 0 0 0 0
Products revenues 0 0 0 0
Services and other revenues 6,593 6,311 10,897 10,692
Operating revenues 2,070,215 2,010,477 4,091,058 4,061,337
Attritional Current Year Claims and Claims Adjustment Expense (1,335,801) (1,334,540) (2,631,324) (2,649,587)
Catastrophe Current Year Claims and Claims Adjustment Expense 5,187 0 (60,877) 0
Losses and loss adjustment expenses, prior accident year 78,934 145,135 227,771 224,102
Amortization of policy acquisition costs (429,109) (415,982) (840,385) (844,173)
Other underwriting expenses (319,633) (274,645) (631,984) (559,893)
Products expenses 0 0 0 0
Services and other expenses (9,456) (6,549) (17,640) (13,162)
Operating Income 60,337 123,896 136,619 218,624
Investing [Member]        
Segment Reporting Information [Line Items]        
Earned premiums 0 0 0 0
Net investment income 228,126 220,454 463,727 437,658
Net investment gains (losses) 580,223 (130,017) 431,152 772,264
Products revenues 0 0 0 0
Services and other revenues 14,064 9,357 9,454 30,203
Operating revenues 822,413 99,794 904,333 1,240,125
Attritional Current Year Claims and Claims Adjustment Expense 0 0 0 0
Catastrophe Current Year Claims and Claims Adjustment Expense 0 0 0 0
Losses and loss adjustment expenses, prior accident year 0 0 0 0
Amortization of policy acquisition costs 0 0 0 0
Other underwriting expenses 0 0 0 0
Products expenses 0 0 0 0
Services and other expenses 0 0 0 0
Operating Income 822,413 99,794 904,333 1,240,125
Markel Ventures [Member]        
Segment Reporting Information [Line Items]        
Earned premiums 0 0 0 0
Net investment income 1,883 2,607 3,377 3,672
Net investment gains (losses) 0 0 0 0
Products revenues 846,925 847,219 1,408,049 1,448,059
Services and other revenues 699,478 603,955 1,266,232 1,142,656
Operating revenues 1,548,286 1,453,781 2,677,658 2,594,387
Attritional Current Year Claims and Claims Adjustment Expense 0 0 0 0
Catastrophe Current Year Claims and Claims Adjustment Expense 0 0 0 0
Losses and loss adjustment expenses, prior accident year 0 0 0 0
Amortization of policy acquisition costs 0 0 0 0
Other underwriting expenses 0 0 0 0
Products expenses (707,381) (693,693) (1,207,289) (1,216,940)
Services and other expenses (633,177) (582,590) (1,160,131) (1,096,034)
Operating Income 207,728 177,498 310,238 281,413
Other Insurance Operations [Member]        
Segment Reporting Information [Line Items]        
Earned premiums 78,069 72,933 150,904 154,081
Net investment income 0 0 0 0
Net investment gains (losses) 0 0 0 0
Products revenues 0 0 0 0
Services and other revenues 83,783 64,858 177,918 118,568
Operating revenues 161,852 137,791 328,822 272,649
Attritional Current Year Claims and Claims Adjustment Expense (36,152) (42,310) (79,337) (92,033)
Catastrophe Current Year Claims and Claims Adjustment Expense 0 0 0 0
Losses and loss adjustment expenses, prior accident year (202) (860) 1,068 (2,804)
Amortization of policy acquisition costs (6,256) (5,657) (12,002) (12,053)
Other underwriting expenses (19,213) (14,011) (37,278) (32,928)
Products expenses 0 0 0 0
Services and other expenses (31,954) (21,924) (64,444) (38,705)
Operating Income 68,075 53,029 136,829 94,126
Corporate [Member]        
Segment Reporting Information [Line Items]        
Earned premiums 0 0 0 0
Net investment income 0 0 0 0
Net investment gains (losses) 0 0 0 0
Products revenues 0 0 0 0
Services and other revenues 0 0 0 0
Operating revenues 0 0 0 0
Attritional Current Year Claims and Claims Adjustment Expense 0 0 0 0
Catastrophe Current Year Claims and Claims Adjustment Expense 0 0 0 0
Losses and loss adjustment expenses, prior accident year 0 0 0 0
Amortization of policy acquisition costs 0 0 0 0
Other underwriting expenses 0 0 0 0
Products expenses 0 0 0 0
Services and other expenses 0 0 0 0
Amortization of acquired intangible assets (51,213) (44,237) (98,155) (88,522)
Operating Income $ (51,213) $ (44,237) $ (98,155) $ (88,522)