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Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Segment Reporting Information [Line Items] |  |  |  |
Earned premiums | $ 2,205,773 | $ 2,110,108 | $ 6,436,838 | $ 6,314,834
Net investment income | 245,675 | 235,477 | 712,779 | 676,807
Products revenues | 607,493 | 612,277 | 2,015,542 | 2,060,336
Services and other revenues | 875,608 | 735,872 | 2,340,109 | 2,037,991
Operating revenues | 3,934,549 | 3,693,734 | 11,505,268 | 11,089,968
Attritional Current Year Claims and Claims Adjustment Expense | (1,389,775) | (1,351,526) | (4,100,436) | (4,093,146)
Catastrophe Current Year Claims and Claims Adjustment Expense | 4,315 | (62,000) | (56,562) | (62,000)
Losses and loss adjustment expenses, prior accident year | 131,634 | 122,914 | 360,473 | 344,212
Amortization of policy acquisition costs | (446,057) | (431,674) | (1,298,444) | (1,287,900)
Other underwriting expenses | (336,444) | (311,882) | (1,005,706) | (904,703)
Products expenses | (555,493) | (549,990) | (1,762,782) | (1,766,930)
Services and other expenses | (721,712) | (609,321) | (1,963,927) | (1,757,222)
Adjusted operating income (loss) | 621,017 | 500,255 | 1,677,884 | 1,562,279
Net investment gains | 432,886 | 917,530 | 864,038 | 1,689,794
Amortization of acquired intangible assets | (44,061) | (46,459) | (142,216) | (134,981)
Interest expense | (50,678) | (53,361) | (155,894) | (151,506)
Net foreign exchange gains (losses) | 19,279 | (111,612) | (245,263) | (51,401)
Income before income taxes | 978,443 | 1,206,353 | 1,998,549 | 2,914,185
Markel Insurance |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned premiums | 2,127,648 | 2,035,773 | 6,207,809 | 6,086,418
Net investment income | 223,409 | 203,767 | 638,654 | 583,349
Products revenues | 0 | 0 | 0 | 0
Services and other revenues | 47,349 | 18,085 | 58,252 | 35,449
Operating revenues | 2,398,406 | 2,257,625 | 6,904,715 | 6,705,216
Attritional Current Year Claims and Claims Adjustment Expense | (1,346,411) | (1,310,108) | (3,977,735) | (3,959,695)
Catastrophe Current Year Claims and Claims Adjustment Expense | 4,315 | (62,000) | (56,562) | (62,000)
Losses and loss adjustment expenses, prior accident year | 129,100 | 119,408 | 356,871 | 343,510
Amortization of policy acquisition costs | (440,568) | (426,149) | (1,280,953) | (1,270,322)
Other underwriting expenses | (318,605) | (294,768) | (950,589) | (854,661)
Products expenses | 0 | 0 | 0 | 0
Services and other expenses | 2,238 | (8,405) | (15,402) | (21,567)
Adjusted operating income (loss) | 428,475 | 275,603 | 980,345 | 880,481
Net investment gains | 389,438 | 709,130 | 745,816 | 1,300,433
Industrial |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned premiums | 0 | 0 | 0 | 0
Net investment income | 0 | 0 | 0 | 0
Products revenues | 425,714 | 438,858 | 1,219,532 | 1,280,894
Services and other revenues | 624,247 | 559,450 | 1,675,718 | 1,503,654
Operating revenues | 1,049,961 | 998,308 | 2,895,250 | 2,784,548
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 | (365,957) | (364,923) | (1,058,275) | (1,073,044)
Services and other expenses | (582,702) | (521,612) | (1,573,396) | (1,454,278)
Adjusted operating income (loss) | 101,302 | 111,773 | 263,579 | 257,226
Net investment gains | 0 | 0 | 0 | 0
Financial |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned premiums | 78,125 | 74,335 | 229,029 | 228,416
Net investment income | 10,020 | 10,012 | 28,578 | 29,797
Products revenues | 0 | 0 | 0 | 0
Services and other revenues | 73,356 | 54,503 | 255,227 | 175,798
Operating revenues | 161,501 | 138,850 | 512,834 | 434,011
Attritional Current Year Claims and Claims Adjustment Expense | (43,364) | (41,418) | (122,701) | (133,451)
Catastrophe Current Year Claims and Claims Adjustment Expense | 0 | 0 | 0 | 0
Losses and loss adjustment expenses, prior accident year | 2,534 | 3,506 | 3,602 | 702
Amortization of policy acquisition costs | (5,489) | (5,525) | (17,491) | (17,578)
Other underwriting expenses | (17,839) | (17,114) | (55,117) | (50,042)
Products expenses | 0 | 0 | 0 | 0
Services and other expenses | (35,936) | 1,353 | (101,687) | (39,436)
Adjusted operating income (loss) | 61,407 | 79,652 | 219,440 | 194,206
Net investment gains | 0 | 10 | 0 | (158)
Consumer and Other |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned premiums | 0 | 0 | 0 | 0
Net investment income | 0 | 0 | 0 | 0
Products revenues | 181,779 | 173,419 | 796,010 | 779,442
Services and other revenues | 109,635 | 91,880 | 312,416 | 284,421
Operating revenues | 291,414 | 265,299 | 1,108,426 | 1,063,863
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 | (189,536) | (185,067) | (704,507) | (693,886)
Services and other expenses | (84,506) | (80,657) | (252,636) | (241,941)
Adjusted operating income (loss) | 17,372 | (425) | 151,283 | 128,036
Net investment gains | 0 | 0 | 0 | 0
Corporate and eliminations |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Earned premiums | 0 | 0 | 0 | 0
Net investment income | 12,246 | 21,698 | 45,547 | 63,661
Products revenues | 0 | 0 | 0 | 0
Services and other revenues | 21,021 | 11,954 | 38,496 | 38,669
Operating revenues | 33,267 | 33,652 | 84,043 | 102,330
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 | (20,806) | 0 | (20,806) | 0
Adjusted operating income (loss) | 12,461 | 33,652 | 63,237 | 102,330
Corporate Operations |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net investment gains | $ 43,448 | $ 208,390 | $ 118,222 | $ 389,519

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