Other Revenues And Other Expenses (Summary Of Other Revenues And Other Expenses By Component) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Revenues and Other Expenses [Line Items]
Other revenues	$ 1,086,758	$ 883,525	$ 710,942
Other expenses	1,046,805	854,871	663,528
Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	12,331	28,632	24,494
Other expenses	40,095	62,834	50,278
Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	1,074,427	854,893	686,448
Other expenses	1,006,710	792,037	613,250
Managing General Agent Operations [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	10,202	23,324	17,399
Other expenses	9,619	22,527	20,382
Life And Annuity [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	617	1,631	1,130
Other expenses	29,057	37,132	28,126
Other Insurance [Member] | Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	1,512	3,677	5,965
Other expenses	1,419	3,175	1,770
Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	755,802	575,353	495,138
Other expenses	677,054	513,668	437,712
Non-Manufacturing [Member] | Non-Insurance Operations [Member] | Markel Ventures Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	291,714	262,767	191,310
Other expenses	301,004	261,551	175,538
Other Non-Insurance [Member] | Non-Insurance Operations [Member]
Other Revenues and Other Expenses [Line Items]
Other revenues	26,911	16,773	0
Other expenses	$ 28,652	$ 16,818	$ 0