Quarterly report pursuant to Section 13 or 15(d)

INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - Narrative (Details)

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INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - Narrative (Details)
storage_unit in Thousands, $ in Thousands, ft² in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2020
ft²
storage_unit
property
state
Jun. 30, 2020
property
Mar. 31, 2020
property
Sep. 30, 2020
USD ($)
ft²
property
storage_unit
state
Sep. 30, 2019
USD ($)
Dec. 31, 2016
property
Schedule of Equity Method Investments [Line Items]            
Number of self storage properties 788     788    
Rentable square feet in self storage properties | ft² 49.5     49.5    
Number of storage units | storage_unit 396     396    
Number of states in which self storage properties are located | state 35     35    
Number of properties acquired 4 4 36 44    
Payments to joint venture | $       $ 3,125 $ 0  
2018 Joint Venture            
Schedule of Equity Method Investments [Line Items]            
Company's equity interest in unconsolidated real estate ventures (percent) 25.00%     25.00%    
2016 Joint Venture            
Schedule of Equity Method Investments [Line Items]            
Company's equity interest in unconsolidated real estate ventures (percent) 25.00%     25.00%    
Joint venture | 2018 Joint Venture            
Schedule of Equity Method Investments [Line Items]            
Company's equity interest in unconsolidated real estate ventures (percent) 25.00%     25.00%    
Joint venture | 2016 Joint Venture            
Schedule of Equity Method Investments [Line Items]            
Payments to joint venture | $       $ 3,100    
Company's equity interest in unconsolidated real estate ventures (percent) 25.00%     25.00%    
Unconsolidated properties | Joint venture | 2018 Joint Venture            
Schedule of Equity Method Investments [Line Items]            
Number of self storage properties 103     103    
Rentable square feet in self storage properties | ft² 7.8     7.8    
Number of storage units | storage_unit 63     63    
Number of states in which self storage properties are located | state 17     17    
Unconsolidated properties | Joint venture | 2016 Joint Venture            
Schedule of Equity Method Investments [Line Items]            
Number of self storage properties 74     74   66
Rentable square feet in self storage properties | ft² 4.9     4.9    
Number of storage units | storage_unit 40     40    
Number of states in which self storage properties are located | state 13     13    
Number of properties acquired       2    
Payments to acquire property | $       $ 12,100