| Document and Entity Information | Nov. 01, 2019 |
| Cover [Abstract] | |
| Entity Registrant Name | MARKETAXESS HOLDINGS INC |
| Amendment Flag | true |
| Amendment Description | On November 4, 2019, the Company filed a Current Report on Form 8-K regarding the Acquisition (the “Original Form 8-K”) and stated that the financial statements required under Item 9.01 of Form 8-K would be filed no later than 71 days after the date on which the Original Form 8-K was required to be filed. This Current Report on Form 8-K amends Items 9.01(a) and 9.01(b) of the Original Form 8-K and contains the required financial statements relating to the Acquisition. |
| Entity Central Index Key | 0001278021 |
| Document Type | 8-K/A |
| Document Period End Date | Nov. 1, 2019 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-34091 |
| Entity Tax Identification Number | 52-2230784 |
| Entity Address, Address Line One | 55 Hudson Yards |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10001 |
| City Area Code | (212) |
| Local Phone Number | 813-6000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Security 12b Title | Common Stock, par value $0.003 per share |
| Trading Symbol | MKTX |
| Security Exchange Name | NASDAQ |
