Related-Party Transactions - Schedule of Equity Interests in Hagerty (Details) - Hagerty, Inc. - shares	Sep. 30, 2026	Sep. 30, 2023
Class of Stock [Line Items]
Percentage of total outstanding		5.00%
Affiliated Entity \| Markel
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	67,163,589
Percentage of total outstanding	29.70%
Affiliated Entity \| Markel \| Total Stockholders' Equity
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	10,944,411
Percentage of total outstanding	9.10%
Affiliated Entity \| Markel \| THG units
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	67,163,589
Percentage of total outstanding	19.40%
Affiliated Entity \| State Farm
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	0
Percentage of total outstanding	0.00%
Affiliated Entity \| State Farm \| Total Stockholders' Equity
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	51,800,000
Percentage of total outstanding	43.00%
Affiliated Entity \| State Farm \| THG units
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	0
Percentage of total outstanding	0.00%
Affiliated Entity \| Class A Common Stock \| Markel
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	10,944,411
Percentage of total outstanding	9.10%
Affiliated Entity \| Class A Common Stock \| State Farm
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	51,800,000
Percentage of total outstanding	43.00%
Affiliated Entity \| Class V Common Stock \| Markel
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	67,163,589
Percentage of total outstanding	30.10%
Affiliated Entity \| Class V Common Stock \| State Farm
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	0
Percentage of total outstanding	0.00%
Affiliated Entity \| Series A Convertible Preferred Stock \| Markel
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	1,590,668
Percentage of total outstanding	18.80%
Affiliated Entity \| Series A Convertible Preferred Stock \| State Farm
Class of Stock [Line Items]
Equity interests in Hagerty (in shares)	5,302,226
Percentage of total outstanding	62.50%