Document and Entity Information - shares
 9 Months Ended
Sep. 30, 2020
Nov. 11, 2020
Document Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2020  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q3  
Entity Registrant Name SmartStop Self Storage REIT, Inc.  
Entity Central Index Key 0001585389  
Entity Current Reporting Status Yes  
Current Fiscal Year End Date --12-31  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Incorporation, State or Country Code MD  
Document Quarterly Report true  
Document Transition Report false  
Entity File Number 000-55617  
Entity Tax Identification Number 46-1722812  
Entity Address, Address Line One 10 Terrace Road  
Entity Address, City or Town Ladera Ranch  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 92694  
City Area Code 877  
Local Phone Number 327-3485  
Entity Interactive Data Current Yes  
Class A Common stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   52,440,201
Class T Common stock    
Document Information [Line Items]    
Entity Common Stock, Shares Outstanding   7,869,657