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v3.25.3

Commitments and Contingencies - Additional Information (Detail) | 9 Months Ended
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Sep. 30, 2025
Commitments and Contingencies Disclosure [Abstract] |
Settlement days of bond transaction | within one to two trading days

X
- Definition Settlement period of bond transaction. + References No definition available. + Details
Name: | mktx_SettlementPeriodOfBondTransaction
Namespace Prefix: | mktx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration