Fair Value Measurements - Summary of Company's Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Investments, Amortized cost	$ 86,417	$ 34,935
Investments, Gross unrealized gains		1,254
Investments, Gross unrealized losses	(2,625)	(111)
Investments, at fair value	83,792	36,078
U.S. Treasuries [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	74,943	24,994
Trading securities, Gross unrealized losses	(534)	(111)
Trading securities, Fair value	74,409	24,883
Mutual Funds Held In Rabbi Trust [Member]
Schedule Of Available For Sale Securities [Line Items]
Trading securities, Amortized cost	11,474	9,941
Trading securities, Gross unrealized gains		1,254
Trading securities, Gross unrealized losses	(2,091)
Trading securities, Fair value	$ 9,383	$ 11,195

Marketable securities accumulated gross unrealized gain before tax.

No definition available.

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

- Definition

Marketable securities accumulated gross unrealized loss before tax.

+ References

No definition available.

+ Details

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

- Definition

Marketable securities amortized cost.

+ References

No definition available.

+ Details

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

- Definition

Trading securities accumulated gross unrealized gain before tax.

+ References

No definition available.

+ Details

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

- Definition

Trading securities accumulated gross unrealized loss before tax.

+ References

No definition available.

+ Details

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

- Definition

Amount of investment in marketable security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

+ Details

Name:	us-gaap_MarketableSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (f)
-URI https://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_TradingSecuritiesDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of investments in debt securities classified as trading.

+ References

No definition available.

+ Details

Name:	us-gaap_TradingSecuritiesDebtAmortizedCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=mktx_MutualFundsHeldInRabbiTrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: