Consolidated Statements Of Income (Loss) And Comprehensive Income (Loss) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
OPERATING REVENUES
Earned premiums		$ 5,049,793		$ 4,712,060		$ 4,247,978
Net investment income		451,888		434,215		405,709
Other-than-temporary impairment losses		0		0		(7,589)
Net realized investment gains (losses), excluding other-than-temporary impairment losses		(1,482)		(11,974)		47,174
Change in fair value of equity securities	[1]	1,603,204		(425,622)		(44,888)
Net investment gains (losses)		1,601,722		(437,596)		(5,303)
Products revenues		1,609,586		1,497,523		951,012
Services and other revenues		813,202		635,083		462,263
Total Operating Revenues		9,526,191		6,841,285		6,061,659
OPERATING EXPENSES
Losses and loss adjustment expenses		2,891,190		2,820,715		2,865,761
Underwriting, acquisition and insurance expenses		1,878,093		1,777,511		1,589,464
Products expenses		1,455,245		1,413,248		850,449
Services and other expenses		675,679		474,924		458,621
Amortization of intangible assets		148,638	[2]	115,930	[3]	80,758	[4]
Impairment of goodwill and intangible assets		0		199,198		0
Total Operating Expenses		7,048,845		6,801,526		5,845,053
Operating Income		2,477,346		39,759		216,606
Interest expense		(171,687)		(154,212)		(132,451)
Net foreign exchange gains (losses)		(2,265)		106,598		3,140
Loss on early extinguishment of debt		(17,586)		0		0
Income (Loss) Before Income Taxes		2,285,808		(7,855)		87,295
Income tax (expense) benefit		(486,346)		(122,498)		313,463
Net Income (Loss)		1,799,462		(130,353)		400,758
Net (income) loss attributable to noncontrolling interests		(8,996)		2,173		(5,489)
Net Income (Loss) to Shareholders	[5]	1,790,466		(128,180)		395,269
OTHER COMPREHENSIVE INCOME (LOSS)
Net holding gains (losses) arising during the period		299,125		(241,325)		787,339
Reclassification adjustments for net gains (losses) included in net income (loss)		(1,148)		7,849		(24,296)
Change in net unrealized gains on available-for-sale investments, net of taxes		297,977		(233,476)		763,043
Change in foreign currency translation adjustments, net of taxes		382		(16,495)		10,449
Change in net actuarial pension loss, net of taxes		5,042		2,341		6,259
Total Other Comprehensive Income (Loss)		303,401		(247,630)		779,751
Comprehensive Income (Loss)		2,102,863		(377,983)		1,180,509
Comprehensive (income) loss attributable to noncontrolling interests		(8,975)		2,213		(5,535)
Comprehensive Income (Loss) to Shareholders		$ 2,093,888		$ (375,770)		$ 1,174,974
NET INCOME (LOSS) PER SHARE
Basic (dollars per share)		$ 129.25		$ (9.55)		$ 25.89
Diluted (dollars per share)	[6]	$ 129.07		$ (9.55)		$ 25.81

[1] Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, equity securities are no longer classified as available-for-sale with unrealized gains and losses recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation. Prior to adopting ASU No. 2016-01, the Company recorded certain investments in equity securities at estimated fair value with changes in fair value recorded in net income.

[2] Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's underwriting segments.

[3] Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's underwriting segments.

[4] Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's underwriting segments.

[5] Effective January 1, 2018, the Company adopted ASU No. 2016-01. As a result, the change in fair value of equity securities is no longer recognized in other comprehensive income; rather, all changes in the fair value of equity securities are now recognized in net income. Prior periods have not been restated to conform to the current presentation.

[6] The impact of restricted stock units and restricted stock of 25 thousand shares was excluded from the computation of diluted earnings per share for the year ended December 31, 2018 because the effect would have been anti-dilutive.