Segment Reporting Disclosures (Summary of Additional Measures for Markel Ventures) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Interest expense		$ 49,438	$ 49,692
Income tax expense		133,731	(18,136)
Markel Ventures [Member]
Segment Reporting Information [Line Items]
Depreciation expense		27,363	25,035
Interest expense	[1]	12,923	11,178
Income tax expense		13,186	8,660
Capital expenditures		31,498	46,013
Intercompany interest expense	[1]	$ 6,600	$ 7,000

[1] Interest expense for the three months ended March 31, 2023 and 2022 included intercompany interest expense of $6.6 million and $7.0 million, respectively, which was eliminated in consolidation.