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 6 Months Ended
Jun. 30, 2020
ft²
property
storage_unit
state
Mar. 31, 2020
property
Jun. 30, 2020
USD ($)
ft²
property
storage_unit
state
Jun. 30, 2019
USD ($)
Dec. 31, 2016
property
Schedule of Equity Method Investments [Line Items]          
Number of self storage properties 784   784    
Rentable square feet in self storage properties | ft² 49.2   49.2    
Number of storage units | storage_unit 394   394    
Number of states in which self storage properties are located | state 35   35    
Number of properties acquired 4 36 40    
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 7.7   7.7    
Number of storage units | storage_unit 64   64    
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