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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)

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