Annual report pursuant to Section 13 and 15(d)

Cover Page

Cover Page - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Feb. 16, 2021
Jun. 30, 2020
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Transition Report false    
Document Period End Date Dec. 31, 2020    
Entity Filer Category Large Accelerated Filer    
Entity Registrant Name MARCUS & MILLICHAP, INC.    
Entity Interactive Data Current Yes    
Title of 12(b) Security Common Stock    
Trading Symbol MMI    
Security Exchange Name NYSE    
Entity File Number 001-36155    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 35-2478370    
Entity Address, Address Line One 23975 Park Sorrento, 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    
Entity Shell Company false    
Entity Small Business false    
Entity Emerging Growth Company false    
Amendment Flag false    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Entity Central Index Key 0001578732    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Public Float     $ 670.5
Entity Common Stock, Shares Outstanding   39,401,976  
ICFR Auditor Attestation Flag true