Deferred Compensation Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation And Retirement Disclosure [Abstract]
Contribution to defined plans	$ 1.9	$ 1.8	$ 1.7
Non-qualified deferred cash incentive plan maximum eligibility percentage of employees	100.00%

Non-qualified deferred cash incentive plan maximum eligibility percentage of employees.

No definition available.

Name:	mktx_NonQualifiedDeferredCashIncentivePlanMaximumEligibilityPercentageOfEmployees
Namespace Prefix:	mktx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration