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Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |
Earned premiums |  | $ 2,121,745 |  | $ 1,956,830 |  | $ 6,120,592 |  | $ 5,549,704 |
Net investment income |  | 192,207 |  | 112,614 |  | 521,235 |  | 301,713 |
Net investment gains (losses) |  | (265,917) |  | (281,483) |  | 591,173 |  | (2,194,525) |
Products revenues |  | 601,524 |  | 586,531 |  | 1,964,332 |  | 1,845,111 |
Services and other revenues |  | 725,627 |  | 691,653 |  | 1,963,779 |  | 1,962,585 |
Operating revenues |  | 3,375,186 |  | 3,066,145 |  | 11,161,111 |  | 7,464,588 |
Losses and loss adjustment expenses, current accident year |  | (1,434,871) |  | (1,266,996) |  | (3,934,969) |  | (3,420,906) |
Losses and loss adjustment expenses, prior accident year |  | 30,546 |  | 81,683 |  | 169,754 |  | 204,411 |
Amortization of policy acquisition costs |  | (437,920) |  | (431,182) |  | (1,298,771) |  | (1,206,325) |
Other underwriting expenses |  | (260,209) |  | (212,090) |  | (772,950) |  | (636,781) |
Products expenses |  | (545,567) |  | (580,830) |  | (1,712,792) |  | (1,726,367) |
Services and other expenses |  | (606,810) |  | (546,384) |  | (1,678,246) |  | (1,693,756) |
Amortization of intangible assets |  | (47,545) | [1] | (43,418) | [2] | (136,367) | [3] | (134,990) | [4]
Segment profit (loss) |  | 72,810 |  | 66,928 |  | 1,796,770 |  | (1,150,126) |
Interest expense |  | (44,553) |  | (47,348) |  | (141,212) |  | (147,090) |
Net foreign exchange gains (losses) |  | 39,246 |  | 113,635 |  | (8,658) |  | 241,706 |
Income (Loss) before income taxes |  | 67,503 |  | 133,215 |  | 1,646,900 |  | (1,055,510) |
Insurance [Member] |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |
Earned premiums |  | 1,848,267 |  | 1,695,029 |  | 5,322,377 |  | 4,742,178 |
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 |  | 1,848,267 |  | 1,695,029 |  | 5,322,377 |  | 4,742,178 |
Losses and loss adjustment expenses, current accident year |  | (1,258,864) |  | (1,100,511) |  | (3,415,860) |  | (2,906,031) |
Losses and loss adjustment expenses, prior accident year |  | 55,374 |  | 53,760 |  | 179,564 |  | 196,093 |
Amortization of policy acquisition costs |  | (369,001) |  | (362,137) |  | (1,096,500) |  | (996,369) |
Other underwriting expenses |  | (250,684) |  | (200,604) |  | (733,334) |  | (596,426) |
Products expenses |  | 0 |  | 0 |  | 0 |  | 0 |
Services and other expenses |  | 0 |  | 0 |  | 0 |  | 0 |
Amortization of intangible assets |  | 0 | [1] | 0 | [2] | 0 | [3] | 0 | [4]
Segment profit (loss) |  | 25,092 |  | 85,537 |  | 256,247 |  | 439,445 |
Reinsurance [Member] |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |
Earned premiums |  | 274,161 |  | 260,535 |  | 799,683 |  | 808,656 |
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 |  | 274,161 |  | 260,535 |  | 799,683 |  | 808,656 |
Losses and loss adjustment expenses, current accident year |  | (176,007) |  | (166,485) |  | (519,109) |  | (514,875) |
Losses and loss adjustment expenses, prior accident year |  | (23,262) |  | 29,505 |  | (6,584) |  | 13,845 |
Amortization of policy acquisition costs |  | (68,919) |  | (68,662) |  | (202,271) |  | (209,541) |
Other underwriting expenses |  | (11,785) |  | (11,638) |  | (38,113) |  | (37,708) |
Products expenses |  | 0 |  | 0 |  | 0 |  | 0 |
Services and other expenses |  | 0 |  | 0 |  | 0 |  | 0 |
Amortization of intangible assets |  | 0 | [1] | 0 | [2] | 0 | [3] | 0 | [4]
Segment profit (loss) |  | (5,812) |  | 43,255 |  | 33,606 |  | 60,377 |
Investing [Member] |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |
Earned premiums |  | 0 |  | 0 |  | 0 |  | 0 |
Net investment income |  | 191,015 |  | 112,297 |  | 518,536 |  | 301,289 |
Net investment gains (losses) |  | (265,917) |  | (281,483) |  | 591,173 |  | (2,194,525) |
Products revenues |  | 0 |  | 0 |  | 0 |  | 0 |
Services and other revenues |  | (5,033) |  | (4,883) |  | (13,791) |  | (27,590) |
Operating revenues |  | (79,935) |  | (174,069) |  | 1,095,918 |  | (1,920,826) |
Losses and loss adjustment expenses, current accident year |  | 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 intangible assets |  | 0 | [1] | 0 | [2] | 0 | [3] | 0 | [4]
Segment profit (loss) |  | (79,935) |  | (174,069) |  | 1,095,918 |  | (1,920,826) |
Markel Ventures [Member] |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |
Earned premiums |  | 0 |  | 0 |  | 0 |  | 0 |
Net investment income |  | 1,192 |  | 317 |  | 2,699 |  | 424 |
Net investment gains (losses) |  | 0 |  | 0 |  | 0 |  | 0 |
Products revenues |  | 601,524 |  | 586,531 |  | 1,964,332 |  | 1,845,111 |
Services and other revenues |  | 644,053 |  | 629,215 |  | 1,770,997 |  | 1,682,318 |
Operating revenues |  | 1,246,769 |  | 1,216,063 |  | 3,738,028 |  | 3,527,853 |
Losses and loss adjustment expenses, current accident year |  | 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 |  | (545,567) |  | (580,830) |  | (1,712,792) |  | (1,726,367) |
Services and other expenses |  | (570,782) |  | (556,207) |  | (1,632,588) |  | (1,524,167) |
Amortization of intangible assets |  | (23,118) | [1] | (18,567) | [2] | (62,528) | [3] | (60,077) | [4]
Segment profit (loss) |  | 107,302 |  | 60,459 |  | 330,120 |  | 217,242 |
Interest expense | [5] | (10,663) |  | (11,921) |  | (36,485) |  | (34,124) |
Other [Member] |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |
Earned premiums |  | (683) | [6] | 1,266 | [7] | (1,468) | [8] | (1,130) | [9]
Net investment income |  | 0 | [6] | 0 | [7] | 0 | [8] | 0 | [9]
Net investment gains (losses) |  | 0 | [6] | 0 | [7] | 0 | [8] | 0 | [9]
Products revenues |  | 0 | [6] | 0 | [7] | 0 | [8] | 0 | [9]
Services and other revenues |  | 86,607 | [6] | 67,321 | [7] | 206,573 | [8] | 307,857 | [9]
Operating revenues |  | 85,924 | [6] | 68,587 | [7] | 205,105 | [8] | 306,727 | [9]
Losses and loss adjustment expenses, current accident year |  | 0 | [6] | 0 | [7] | 0 | [8] | 0 | [9]
Losses and loss adjustment expenses, prior accident year |  | (1,566) | [6] | (1,582) | [7] | (3,226) | [8] | (5,527) | [9]
Amortization of policy acquisition costs |  | 0 | [6] | (383) | [7] | 0 | [8] | (415) | [9]
Other underwriting expenses |  | 2,260 | [6] | 152 | [7] | (1,503) | [8] | (2,647) | [9]
Products expenses |  | 0 | [6] | 0 | [7] | 0 | [8] | 0 | [9]
Services and other expenses |  | (36,028) | [6] | 9,823 | [7] | (45,658) | [8] | (169,589) | [9]
Amortization of intangible assets |  | (24,427) | [1],[6] | (24,851) | [2],[7] | (73,839) | [3],[8] | (74,913) | [4],[9]
Segment profit (loss) |  | 26,163 | [6] | 51,746 | [7] | 80,879 | [8] | 53,636 | [9]
Underwriting Segments [Member] |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |
Amortization of intangible assets |  | $ 9,100 | [6] | $ 9,600 | [2] | $ 28,000 | [3] | $ 29,000 | [4]
[1] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets attributable to the Company's underwriting segments, included in Other, was $9.1 million for the quarter ended September 30, 2023
[2] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets attributable to the Company's underwriting segments, included in Other, was $9.6 million for the quarter ended September 30, 2022
[3] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets attributable to the Company's underwriting segments, included in Other, was $28.0 million for the nine months ended September 30, 2023.
[4] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets attributable to the Company's underwriting segments, included in Other, was $29.0 million for the nine months ended September 30, 2022.
[5] | Interest expense for the quarter and nine months ended September 30, 2023 included intercompany interest expense of $6.6 million and $19.9 million, respectively. Interest expense for the quarter and nine months ended September 30, 2022 included intercompany interest expense of $6.6 million and $20.7 million, respectively. Intercompany interest expense was eliminated in consolidation.
[6] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment, as well as amortization of intangible assets attributable to underwriting segments, which is not allocated between the Insurance and Reinsurance segments.
[7] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment, as well as amortization of intangible assets attributable to underwriting segments, which is not allocated between the Insurance and Reinsurance segments.
[8] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment, as well as amortization of intangible assets attributable to underwriting segments, which is not allocated between the Insurance and Reinsurance segments.
[9] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment, as well as amortization of intangible assets attributable to underwriting segments, which is not allocated between the Insurance and Reinsurance segments.

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