v3.26.3
Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Segment Reporting [Line Items]        
Earned premiums $ 2,275,508 $ 2,205,773 $ 6,396,172 $ 6,436,838
Net investment income 258,115 245,675 770,128 712,779
Products revenues 666,749 607,493 2,098,635 2,015,542
Services and other revenues 957,831 875,608 2,462,310 2,340,109
Operating revenues 4,158,203 3,934,549 11,727,245 11,505,268
Attritional Current Year Claims and Claims Adjustment Expense (1,316,570) (1,389,775) (3,864,948) (4,100,436)
Catastrophe Current Year Claims and Claims Adjustment Expense (74,555) [1] 4,315 (150,566) [1] (56,562)
Losses and loss adjustment expenses, prior accident year 115,520 131,634 385,941 360,473
Amortization of policy acquisition costs (456,363) (446,057) (1,289,869) (1,298,444)
Other underwriting expenses (341,816) (336,444) (983,949) (1,005,706)
Products expenses (603,322) (555,493) (1,844,210) (1,762,782)
Services and other expenses (773,700) (721,712) (2,338,380) (1,963,927)
Adjusted operating income (loss) 707,397 621,017 1,641,264 1,677,884
Net investment gains (losses) (280,909) 432,886 159,054 864,038
Amortization of acquired intangible assets (43,256) (44,061) (130,070) (142,216)
Interest expense (50,864) (50,678) (154,140) (155,894)
Net foreign exchange gains (losses) 14,386 19,279 79,041 (245,263)
Income Before Income Taxes 346,754 978,443 1,595,149 1,998,549
Markel Insurance        
Segment Reporting [Line Items]        
Earned premiums 2,190,244 2,127,648 6,151,944 6,207,809
Net investment income 233,569 223,409 694,411 638,654
Products revenues 0 0 0 0
Services and other revenues 20,095 47,349 33,152 58,252
Operating revenues 2,443,908 2,398,406 6,879,507 6,904,715
Attritional Current Year Claims and Claims Adjustment Expense (1,273,767) (1,346,411) (3,723,371) (3,977,735)
Catastrophe Current Year Claims and Claims Adjustment Expense (74,555) [1] 4,315 (150,566) [1] (56,562)
Losses and loss adjustment expenses, prior accident year 113,574 129,100 387,073 356,871
Amortization of policy acquisition costs (451,716) (440,568) (1,272,787) (1,280,953)
Other underwriting expenses (325,526) (318,605) (929,671) (950,589)
Products expenses 0 0 0 0
Services and other expenses (11,021) 2,238 (23,308) (15,402)
Adjusted operating income (loss) 420,897 428,475 1,166,877 980,345
Net investment gains (losses) (215,268) 389,438 261,102 745,816
Industrial        
Segment Reporting [Line Items]        
Earned premiums 0 0 0 0
Net investment income 0 0 0 0
Products revenues 486,465 425,714 1,306,085 1,219,532
Services and other revenues 695,137 624,247 1,796,643 1,675,718
Operating revenues 1,181,602 1,049,961 3,102,728 2,895,250
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 (424,546) (365,957) (1,165,677) (1,058,275)
Services and other expenses (625,914) (582,702) (1,681,189) (1,573,396)
Adjusted operating income (loss) 131,142 101,302 255,862 263,579
Net investment gains (losses) 0 0 0 0
Financial        
Segment Reporting [Line Items]        
Earned premiums 85,264 78,125 244,228 229,029
Net investment income 10,803 10,020 29,404 28,578
Products revenues 0 0 0 0
Services and other revenues 85,965 73,356 241,278 255,227
Operating revenues 182,032 161,501 514,910 512,834
Attritional Current Year Claims and Claims Adjustment Expense (42,803) (43,364) (141,577) (122,701)
Catastrophe Current Year Claims and Claims Adjustment Expense 0 0 0 0
Losses and loss adjustment expenses, prior accident year 1,946 2,534 (1,132) 3,602
Amortization of policy acquisition costs (4,647) (5,489) (17,082) (17,491)
Other underwriting expenses (16,290) (17,839) (54,278) (55,117)
Products expenses 0 0 0 0
Services and other expenses (40,164) (35,936) (333,502) (101,687)
Adjusted operating income (loss) 80,074 61,407 (32,661) 219,440
Net investment gains (losses) (10,118) 0 (9,749) 0
Consumer and Other        
Segment Reporting [Line Items]        
Earned premiums 0 0 0 0
Net investment income 0 0 0 0
Products revenues 180,284 181,779 792,550 796,010
Services and other revenues 116,025 109,635 336,230 312,416
Operating revenues 296,309 291,414 1,128,780 1,108,426
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 (178,776) (189,536) (678,533) (704,507)
Services and other expenses (86,312) (84,506) (257,125) (252,636)
Adjusted operating income (loss) 31,221 17,372 193,122 151,283
Net investment gains (losses) 0 0 0 0
Corporate and eliminations        
Segment Reporting [Line Items]        
Earned premiums 0 0 0 0
Net investment income 13,743 12,246 46,313 45,547
Products revenues 0 0 0 0
Services and other revenues 40,609 21,021 55,007 38,496
Operating revenues 54,352 33,267 101,320 84,043
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 (10,289) (20,806) (43,256) (20,806)
Adjusted operating income (loss) 44,063 12,461 58,064 63,237
Corporate Operations        
Segment Reporting [Line Items]        
Net investment gains (losses) $ (55,523) $ 43,448 $ (92,299) $ 118,222
[1] Catastrophe current accident year losses and loss adjustment expenses were related to the Middle East conflict.