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)
ft² in Millions, $ in Millions
3 Months Ended
Mar. 31, 2019
USD ($)
ft²
storage_unit
state
property
Dec. 31, 2016
property
Schedule of Equity Method Investments [Line Items]    
Number of self storage properties 706  
Rentable square feet in self storage properties | ft² 44.7  
Number of storage units owned and operated | storage_unit 361,000  
Number of states in which self storage properties are owned | state 34  
Corporate Joint Venture | 2016 Joint Venture    
Schedule of Equity Method Investments [Line Items]    
Number of self storage properties   66
Unconsolidated Properties | Corporate 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 7.7  
Number of storage units owned and operated | storage_unit 63,000  
Number of states in which self storage properties are owned | state 17  
Unconsolidated Properties | Corporate Joint Venture | 2016 Joint Venture    
Schedule of Equity Method Investments [Line Items]    
Number of self storage properties 72  
Rentable square feet in self storage properties | ft² 4.9  
Number of storage units owned and operated | storage_unit 40,000  
Number of states in which self storage properties are owned | state 13  
Number of self storage properties sold 1  
Gross selling price of self storage properties sold | $ $ 4.1