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Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Segment Reporting Information [Line Items] |  |
Earned premiums | $ 2,127,627 | $ 1,967,704
Net investment income | 218,269 | 159,335
Net investment gains | 902,281 | 372,563
Products revenues | 600,840 | 577,926
Services and other revenues | 617,638 | 565,861
Operating revenues | 4,466,655 | 3,643,389
Losses and loss adjustment expenses, current accident year | (1,364,770) | (1,244,331)
Losses and loss adjustment expenses, prior accident year | 77,023 | 71,317
Amortization of policy acquisition costs | (434,587) | (422,132)
Other underwriting expenses | (304,165) | (253,573)
Products expenses | (523,247) | (515,756)
Services and other expenses | (536,838) | (480,619)
Amortization of acquired intangible assets | (44,285) | (44,399)
Operating Income | 1,335,786 | 753,896
Interest expense | (45,548) | (49,438)
Net foreign exchange gains (losses) | 51,500 | (32,928)
Income (Loss) before income taxes | 1,341,738 | 671,530
Insurance [Member] |  |
Segment Reporting Information [Line Items] |  |
Earned premiums | 1,874,461 | 1,710,924
Net investment income | 0 | 0
Net investment gains | 0 | 0
Products revenues | 0 | 0
Services and other revenues | 0 | 0
Operating revenues | 1,874,461 | 1,710,924
Losses and loss adjustment expenses, current accident year | (1,201,555) | (1,077,546)
Losses and loss adjustment expenses, prior accident year | 97,181 | 62,628
Amortization of policy acquisition costs | (373,778) | (360,354)
Other underwriting expenses | (288,999) | (239,148)
Products expenses | 0 | 0
Services and other expenses | 0 | 0
Operating Income | 107,310 | 96,504
Reinsurance [Member] |  |
Segment Reporting Information [Line Items] |  |
Earned premiums | 253,339 | 257,234
Net investment income | 0 | 0
Net investment gains | 0 | 0
Products revenues | 0 | 0
Services and other revenues | 0 | 0
Operating revenues | 253,339 | 257,234
Losses and loss adjustment expenses, current accident year | (163,215) | (166,785)
Losses and loss adjustment expenses, prior accident year | (3,398) | 8,704
Amortization of policy acquisition costs | (60,809) | (61,778)
Other underwriting expenses | (13,907) | (13,141)
Products expenses | 0 | 0
Services and other expenses | 0 | 0
Operating Income | 12,010 | 24,234
Investing [Member] |  |
Segment Reporting Information [Line Items] |  |
Earned premiums | 0 | 0
Net investment income | 217,204 | 158,594
Net investment gains | 902,281 | 372,563
Products revenues | 0 | 0
Services and other revenues | 20,846 | (2,380)
Operating revenues | 1,140,331 | 528,777
Losses and loss adjustment expenses, current accident year | 0 | 0
Losses and loss adjustment expenses, prior accident year | 0 | 0
Amortization of policy acquisition costs | 0 | 0
Other underwriting expenses | 0 | 0
Products expenses | 0 | 0
Services and other expenses | 0 | 0
Operating Income | 1,140,331 | 528,777
Markel Ventures [Member] |  |
Segment Reporting Information [Line Items] |  |
Earned premiums | 0 | 0
Net investment income | 1,065 | 741
Net investment gains | 0 | 0
Products revenues | 600,840 | 577,926
Services and other revenues | 538,701 | 526,013
Operating revenues | 1,140,606 | 1,104,680
Losses and loss adjustment expenses, current accident year | 0 | 0
Losses and loss adjustment expenses, prior accident year | 0 | 0
Amortization of policy acquisition costs | 0 | 0
Other underwriting expenses | 0 | 0
Products expenses | (523,247) | (515,756)
Services and other expenses | (513,444) | (496,746)
Operating Income | 103,915 | 92,178
Other Insurance Operations [Member] |  |
Segment Reporting Information [Line Items] |  |
Earned premiums | (173) | (454)
Net investment income | 0 | 0
Net investment gains | 0 | 0
Products revenues | 0 | 0
Services and other revenues | 58,091 | 42,228
Operating revenues | 57,918 | 41,774
Losses and loss adjustment expenses, current accident year | 0 | 0
Losses and loss adjustment expenses, prior accident year | (16,760) | (15)
Amortization of policy acquisition costs | 0 | 0
Other underwriting expenses | (1,259) | (1,284)
Products expenses | 0 | 0
Services and other expenses | (23,394) | 16,127
Operating Income | 16,505 | 56,602
Corporate [Member] |  |
Segment Reporting Information [Line Items] |  |
Earned premiums | 0 | 0
Net investment income | 0 | 0
Net investment gains | 0 | 0
Products revenues | 0 | 0
Services and other revenues | 0 | 0
Operating revenues | 0 | 0
Losses and loss adjustment expenses, current accident year | 0 | 0
Losses and loss adjustment expenses, prior accident year | 0 | 0
Amortization of policy acquisition costs | 0 | 0
Other underwriting expenses | 0 | 0
Products expenses | 0 | 0
Services and other expenses | 0 | 0
Amortization of acquired intangible assets | (44,285) | (44,399)
Operating Income | $ (44,285) | $ (44,399)

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