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, ft² in Millions
Mar. 31, 2021
ft²
storage_unit
property
state
Dec. 31, 2016
property
Schedule of Equity Method Investments [Line Items]    
Number of self storage properties | property 844  
Rentable square feet in self storage properties | ft² 53.5  
Number of storage units | storage_unit 425  
Number of states in which self storage properties are located | state 36  
Unconsolidated properties | Joint venture | 2018 Joint Venture    
Schedule of Equity Method Investments [Line Items]    
Number of self storage properties | property 103  
Rentable square feet in self storage properties | ft² 7.8  
Number of storage units | storage_unit 64  
Number of states in which self storage properties are located | state 17  
Unconsolidated properties | Joint venture | 2016 Joint Venture    
Schedule of Equity Method Investments [Line Items]    
Number of self storage properties | property 74 66
Rentable square feet in self storage properties | ft² 4.9  
Number of storage units | storage_unit 40  
Number of states in which self storage properties are located | state 13