Markel Corporation (Parent Company Only) Financial Information (Schedule Of Condensed Statements Of Income And Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net investment income													$ 353,213	$ 363,230	$ 317,373
Other-than-temporary impairment losses													(44,481)	(4,784)	(4,706)
Net realized investment gains, excluding other-than-temporary impairment losses													150,961	50,784	67,858
Net realized investment gains													106,480	46,000	63,152
Other													1,086,758	883,525	710,942
Total Operating Revenues	$ 1,420,460	$ 1,342,764	$ 1,304,605	$ 1,302,154	$ 1,335,755	$ 1,299,286	$ 1,258,971	$ 1,239,655	$ 1,279,785	$ 1,191,665	$ 1,031,769	$ 819,864	5,369,983	5,133,667	4,323,083
Interest expense													118,301	117,442	114,004
Other expenses													1,046,805	854,871	663,528
Total Operating Expenses													4,509,577	4,575,847	3,847,336
Income tax benefit													152,963	116,690	77,898
Net Income to Shareholders	197,892	102,519	91,369	190,992	117,595	75,803	40,068	87,716	98,764	65,599	27,756	88,902	582,772	321,182	281,021
Net holding gains (losses) arising during the period													(240,170)	687,735	225,545
Reclassification adjustments for net losses included in net income to shareholders													(80,482)	(26,161)	(40,830)
Change in net unrealized gains on investments, net of taxes													(320,492)	661,747	184,574
Change in foreign currency translation adjustments, net of taxes													(29,278)	(32,241)	(10,143)
Total Other Comprehensive Income (Loss)													(350,122)	614,756	178,496
Comprehensive Income to Shareholders	$ 134,984	$ (51,143)	$ (132,925)	$ 281,807	$ 418,571	$ 36,502	$ 250,588	$ 230,273	$ 206,450	$ 144,409	$ (149,054)	$ 257,684	232,723	935,934	459,489
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net investment income													2,565	5,354	21,946
Dividends on common stock of consolidated subsidiaries													187,496	217,121	806,233
Other-than-temporary impairment losses													(3,455)	(120)	(15)
Net realized investment gains, excluding other-than-temporary impairment losses													75,000	3,873	67,232
Net realized investment gains													71,545	3,753	67,217
Other													0	0	1
Total Operating Revenues													261,606	226,228	895,397
Interest expense													95,620	94,097	92,743
Other expenses													11,287	2,685	2,617
Total Operating Expenses													106,907	96,782	95,360
Income Before Equity in Undistributed Earnings of Consolidated Subsidiaries and Income Taxes													154,699	129,446	800,037
Equity in undistributed earnings of consolidated subsidiaries													407,489	163,341	(520,323)
Income tax benefit													(20,584)	(28,395)	(1,307)
Net Income to Shareholders													582,772	321,182	281,021
Net holding gains (losses) arising during the period													(41,861)	32,118	66,623
Consolidated subsidiaries' net holding gains (losses) arising during the period													(198,309)	655,617	158,922
Consolidated subsidiaries' change in unrealized other-than-temporary impairment losses on fixed maturities arising during the period													160	173	(141)
Reclassification adjustments for net losses included in net income to shareholders													(45,273)	(1,874)	(43,220)
Consolidated subsidiaries' reclassification adjustments for net gains (losses) included in net income to shareholders													(35,209)	(24,287)	2,390
Change in net unrealized gains on investments, net of taxes													(320,492)	661,747	184,574
Change in foreign currency translation adjustments, net of taxes													2,970	1,949	(2,670)
Consolidated subsidiaries' change in foreign currency translation adjustments, net of taxes													(32,175)	(34,194)	(7,501)
Consolidated subsidiaries' change in net actuarial pension loss, net of taxes													(352)	(14,750)	4,065
Total Other Comprehensive Income (Loss)													(350,049)	614,752	178,468
Comprehensive Income to Shareholders													$ 232,723	$ 935,934	$ 459,489