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Discontinued Operations - Additional Information (Detail) (USD $)
1 Months Ended 12 Months Ended
Oct. 31, 2013
Dec. 31, 2013
Discontinued Operation Income Loss From Discontinued Operation Disclosures [Abstract]    
Recognized gain, net of tax $ 7,600,000us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax $ 7,642,000us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax
Stock purchase agreement 100.00%mktx_DiscontinuedOperationsPercentageOfSharesSold  
Aggregate purchase price $ 11,000,000us-gaap_ProceedsFromDivestitureOfBusinesses