Summary of Significant Accounting Policies - Additional Information (Detail)
shares in Millions
 3 Months Ended 6 Months Ended 9 Months Ended 12 Months Ended
Oct. 30, 2020
USD ($)
shares
Sep. 30, 2020
USD ($)
shares
Sep. 30, 2019
USD ($)
Jun. 30, 2020
USD ($)
shares
Sep. 30, 2020
USD ($)
Trademark
Segment
Sep. 30, 2019
USD ($)
Dec. 31, 2019
USD ($)
shares
Jan. 01, 2020
USD ($)
Jun. 28, 2019
USD ($)
Summary Of Significant Accounting Policies [Line Items]                  
Investments in Managed REITs                 $ 5,600,000
Payments to acquire intangible assets         $ 0 $ 13,600,000      
Business acquisition, transaction costs   $ 470,000 $ 26,000   594,000 194,000      
Impairment losses of real property assets recognized   0 0   0 0      
Goodwill   53,643,331     53,643,331   $ 78,372,980   $ 78,372,980
Trademarks acquired amount     0     0      
Trademarks acquired   16,229,412     16,229,412   19,688,167    
Gross amounts of lease intangibles   46,600,000     46,600,000   46,800,000    
Accumulated amortization   45,200,000     45,200,000   40,400,000    
Redemptions of common stock   $ 700,000   $ 1,300,000 $ 700,000   $ 4,900,000 $ 400,000  
Redemptions of common stock (in shares) | shares   0.1   0.1     0.5    
Minimum percentage of ordinary taxable income to be distributed to stockholders         90.00%        
Number of reportable business segments | Segment         2        
Subsequent Event                  
Summary Of Significant Accounting Policies [Line Items]                  
Redemptions of common stock $ 1,300,000                
Redemptions of common stock (in shares) | shares 0.1                
Real Estate Investment                  
Summary Of Significant Accounting Policies [Line Items]                  
Gains (losses) on exchange rate changes in equity investments recorded in other income (expense)   $ 300,000 $ 200,000   $ (300,000) $ 700,000      
Class T Common stock                  
Summary Of Significant Accounting Policies [Line Items]                  
Monthly stockholder servicing fee accrual description         accrues daily in an amount equal to 1/365th of 1% of the purchase price per share        
Redeemable Common Stock                  
Summary Of Significant Accounting Policies [Line Items]                  
Redemptions of common stock             $ 4,500,000    
Non Revolving Debt                  
Summary Of Significant Accounting Policies [Line Items]                  
Debt issuance cost, gross   11,900,000     $ 11,900,000   11,900,000    
Accumulated amortization of debt issuance costs   7,100,000     7,100,000   4,300,000    
Self Storage                  
Summary Of Significant Accounting Policies [Line Items]                  
Goodwill   45,300,000     45,300,000        
Total estimated future amortization expense of intangible assets, year 2020   25,000,000,000     25,000,000,000        
Total estimated future amortization expense of intangible assets, year 2021   100,000     100,000        
Total estimated future amortization expense of intangible assets, year 2022   100,000     100,000        
Total estimated future amortization expense of intangible assets, year 2023   100,000     100,000        
Total estimated future amortization expense of intangible assets, year 2024   100,000     100,000        
Total estimated future amortization expense of intangible assets, thereafter   1,000,000.0     1,000,000.0        
Self Administration Transaction                  
Summary Of Significant Accounting Policies [Line Items]                  
Total estimated future amortization expense of intangible assets, year 2020   1,000,000.0     1,000,000.0        
Total estimated future amortization expense of intangible assets, year 2021   2,900,000     2,900,000        
Total estimated future amortization expense of intangible assets, year 2022   2,900,000     2,900,000        
Total estimated future amortization expense of intangible assets, year 2023   2,900,000     2,900,000        
Total estimated future amortization expense of intangible assets, year 2024   1,800,000     1,800,000        
Total estimated future amortization expense of intangible assets, thereafter   300,000     $ 300,000        
Minimum                  
Summary Of Significant Accounting Policies [Line Items]                  
Estimated useful life         3 years        
Maximum                  
Summary Of Significant Accounting Policies [Line Items]                  
Estimated useful life         5 years        
SmartStop Trademark                  
Summary Of Significant Accounting Policies [Line Items]                  
Amortization period of intangible assets         8 years        
Strategic Storage Trademark                  
Summary Of Significant Accounting Policies [Line Items]                  
Amortization period of intangible assets         7 years        
Total estimated future amortization expense of intangible assets, year 2020   35,000     $ 35,000        
Total estimated future amortization expense of intangible assets, year 2021   140,000     140,000        
Total estimated future amortization expense of intangible assets, year 2022   140,000     140,000        
Total estimated future amortization expense of intangible assets, year 2023   140,000     140,000        
Total estimated future amortization expense of intangible assets, year 2024   70,000     70,000        
Total estimated future amortization expense of intangible assets, thereafter   0     $ 0        
Trademarks                  
Summary Of Significant Accounting Policies [Line Items]                  
Amortization period of intangible assets         15 years        
Self Administration Transaction                  
Summary Of Significant Accounting Policies [Line Items]                  
Goodwill   78,400,000     $ 78,400,000        
Trademarks acquired   19,800,000     $ 19,800,000        
Number of trademarks acquired | Trademark         2        
Gross amounts of lease intangibles   18,100,000     $ 18,100,000   26,500,000    
Accumulated amortization   6,300,000     $ 6,300,000   $ 2,900,000    
Former Dealer Manager                  
Summary Of Significant Accounting Policies [Line Items]                  
Underwriting commission         10.00%        
Maximum former dealer manager commission fee percentage of proceeds from Primary Offering         3.00%        
Former Dealer Manager | Class T Common stock                  
Summary Of Significant Accounting Policies [Line Items]                  
Monthly stockholder servicing fee accrual description         accrues daily in an amount equal to 1/365th of 1% of the purchase price per share   accrues daily in an amount equal to 1/365th of 1% of the purchase price per share    
Primary Offering Former Dealer Manager Agreement | Class T Common stock                  
Summary Of Significant Accounting Policies [Line Items]                  
Percentage of gross proceeds from sale of shares         10.00%        
Primary Offering Former Dealer Manager Agreement | Class A Common stock                  
Summary Of Significant Accounting Policies [Line Items]                  
Percentage of gross proceeds from sale of shares         10.00%        
Investments in and Advances to Managed REITs                  
Summary Of Significant Accounting Policies [Line Items]                  
Investments in Managed REITs   7,900,000     $ 7,900,000   $ 5,800,000    
Investments in and Advances to Managed REITs | Mangaed REITs                  
Summary Of Significant Accounting Policies [Line Items]                  
Receivables due from related parties   $ 320,000     $ 320,000   $ 275,000