| Document and Entity Information | Aug. 06, 2020 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001578732 |
| Document Type | 8-K |
| Document Period End Date | Aug. 6, 2020 |
| Entity Registrant Name | MARCUS & MILLICHAP, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-36155 |
| Entity Tax Identification Number | 35-2478370 |
| Entity Address, Address Line One | 23975 Park Sorrento |
| Entity Address, Address Line Two | Suite 400 |
| Entity Address, City or Town | Calabasas |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 91302 |
| City Area Code | (818) |
| Local Phone Number | 212-2250 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.0001 per share |
| Trading Symbol | MMI |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
