Markel Corporation (Parent Company Only) Financial Information (Schedule of Condensed Balance Sheets - Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Fixed maturities, amortized cost	$ 9,038,158	$ 9,929,137
Equity securities, cost	2,208,834	1,951,658
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Fixed maturities, amortized cost	35,475	47,346
Equity securities, cost	$ 204,289	$ 193,864