v3.25.1
Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Segment Reporting Information [Line Items]    
Earned premiums $ 2,089,374 $ 2,127,627
Net investment income 237,095 218,269
Net investment gains (losses) (149,071) 902,281
Products revenues 561,124 600,840
Services and other revenues 660,583 617,638
Operating revenues 3,399,105 4,466,655
Attritional Current Year Claims and Claims Adjustment Expense (1,338,709) (1,364,770)
Catastrophe Current Year Claims and Claims Adjustment Expense (66,063) 0
Losses and loss adjustment expenses, prior accident year 150,107 77,023
Amortization of policy acquisition costs (417,009) (434,587)
Other underwriting expenses (330,429) (304,165)
Products expenses (499,908) (523,247)
Services and other expenses (567,628) (536,838)
Amortization of acquired intangible assets (46,942) (44,285)
Operating Income 282,524 1,335,786
Interest expense (52,140) (45,548)
Net foreign exchange gains (losses) (72,633) 51,500
Income before income taxes 157,751 1,341,738
Insurance [Member]    
Segment Reporting Information [Line Items]    
Earned premiums 1,817,851 1,874,461
Net investment income 0 0
Net investment gains (losses) 0 0
Products revenues 0 0
Services and other revenues 0 0
Operating revenues 1,817,851 1,874,461
Attritional Current Year Claims and Claims Adjustment Expense (1,156,956) (1,201,555)
Catastrophe Current Year Claims and Claims Adjustment Expense (64,113) 0
Losses and loss adjustment expenses, prior accident year 126,452 97,181
Amortization of policy acquisition costs (354,507) (373,778)
Other underwriting expenses (315,511) (288,999)
Products expenses 0 0
Services and other expenses 0 0
Operating Income 53,216 107,310
Reinsurance [Member]    
Segment Reporting Information [Line Items]    
Earned premiums 271,549 253,339
Net investment income 0 0
Net investment gains (losses) 0 0
Products revenues 0 0
Services and other revenues 0 0
Operating revenues 271,549 253,339
Attritional Current Year Claims and Claims Adjustment Expense (181,753) (163,215)
Catastrophe Current Year Claims and Claims Adjustment Expense (1,950) 0
Losses and loss adjustment expenses, prior accident year 14,258 (3,398)
Amortization of policy acquisition costs (62,502) (60,809)
Other underwriting expenses (14,569) (13,907)
Products expenses 0 0
Services and other expenses 0 0
Operating Income 25,033 12,010
Investing [Member]    
Segment Reporting Information [Line Items]    
Earned premiums 0 0
Net investment income 235,601 217,204
Net investment gains (losses) (149,071) 902,281
Products revenues 0 0
Services and other revenues (4,610) 20,846
Operating revenues 81,920 1,140,331
Attritional Current Year Claims and Claims Adjustment Expense 0 0
Catastrophe Current Year Claims and Claims Adjustment Expense 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 81,920 1,140,331
Markel Ventures [Member]    
Segment Reporting Information [Line Items]    
Earned premiums 0 0
Net investment income 1,494 1,065
Net investment gains (losses) 0 0
Products revenues 561,124 600,840
Services and other revenues 566,754 538,701
Operating revenues 1,129,372 1,140,606
Attritional Current Year Claims and Claims Adjustment Expense 0 0
Catastrophe Current Year Claims and Claims Adjustment Expense 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 (499,908) (523,247)
Services and other expenses (526,954) (513,444)
Operating Income 102,510 103,915
Other Insurance Operations [Member]    
Segment Reporting Information [Line Items]    
Earned premiums (26) (173)
Net investment income 0 0
Net investment gains (losses) 0 0
Products revenues 0 0
Services and other revenues 98,439 58,091
Operating revenues 98,413 57,918
Attritional Current Year Claims and Claims Adjustment Expense 0 0
Catastrophe Current Year Claims and Claims Adjustment Expense 0 0
Losses and loss adjustment expenses, prior accident year 9,397 (16,760)
Amortization of policy acquisition costs 0 0
Other underwriting expenses (349) (1,259)
Products expenses 0 0
Services and other expenses (40,674) (23,394)
Operating Income 66,787 16,505
Corporate [Member]    
Segment Reporting Information [Line Items]    
Earned premiums 0 0
Net investment income 0 0
Net investment gains (losses) 0 0
Products revenues 0 0
Services and other revenues 0 0
Operating revenues 0 0
Attritional Current Year Claims and Claims Adjustment Expense 0 0
Catastrophe Current Year Claims and Claims Adjustment Expense 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 (46,942) (44,285)
Operating Income $ (46,942) $ (44,285)