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
Mar. 31, 2020
USD ($)
ft²
property
state
storage_unit
Mar. 31, 2019
USD ($)
Dec. 31, 2016
property
Schedule of Equity Method Investments [Line Items]      
Number of self storage properties 780    
Rentable square feet in self storage properties | ft² 48.9    
Number of storage units | storage_unit 392    
Number of states in which self storage properties are located | state 35    
Number of properties acquired 36    
Payments to joint venture | $ $ 3,125 $ 0  
Joint Venture | 2016 Joint Venture      
Schedule of Equity Method Investments [Line Items]      
Number of self storage properties     66
Unconsolidated real estate ventures | Joint Venture      
Schedule of Equity Method Investments [Line Items]      
Number of self storage properties 177    
Rentable square feet in self storage properties | ft² 12.7    
Number of storage units | storage_unit 104    
Number of states in which self storage properties are located | state 21    
Company's equity interest in unconsolidated real estate ventures (percent) 25.00%    
Unconsolidated real estate ventures | Joint Venture | 2018 Joint Venture      
Schedule of Equity Method Investments [Line Items]      
Number of self storage properties 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 real estate ventures | Joint Venture | 2016 Joint Venture      
Schedule of Equity Method Investments [Line Items]      
Number of self storage properties 74    
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    
Number of properties acquired 2    
Payments to acquire property | $ $ 12,100    
Payments to joint venture | $ $ 3,100