Initial settlement payment amount.

No definition available.

Name:	mktx_InitialSettlementPaymentAmount
Namespace Prefix:	mktx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Stock repurchase program additional authorized repurchase amount1.

+ References

No definition available.

+ Details

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Namespace Prefix:	mktx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount remaining authorized for purchase of share under share repurchase plan. Includes, but is not limited to, repurchase of stock and unit of ownership.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
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- Definition

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ References

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Balance Type:	na
Period Type:	duration

- Definition

Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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- Details

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- Details

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- Details

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Share Repurchase Programs - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Mar. 31, 2025	Jun. 30, 2026	Dec. 31, 2025	Dec. 09, 2025	Aug. 31, 2024
Equity Class Of Treasury Stock [Line Items]
Shares repurchase program, value	$ 36,687	$ 38,077
2024 Repurchase Program [Member]
Equity Class Of Treasury Stock [Line Items]
Shares repurchase program authorized additional, value						$ 200,000
2025 Repurchase Program and 2024 Repurchase Program [Member]
Equity Class Of Treasury Stock [Line Items]
Shares repurchase program authorized additional, value				$ 400,000
Shares repurchase program, value			$ 60,000
Shares repurchase program, shares			359,782
Accelerated Share Repurchase Program [Member]
Equity Class Of Treasury Stock [Line Items]
Initial Settlement Payment Amount					$ 300,000
2025 Repurchase Program
Equity Class Of Treasury Stock [Line Items]
Share Repurchase program, remaining capacity			$ 205,000