Quarterly report pursuant to Section 13 or 15(d)

INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURE - Narrative (Details)

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INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURE - Narrative (Details)
storage_unit in Thousands, $ in Thousands, ft² in Millions
3 Months Ended
Mar. 31, 2018
USD ($)
ft²
storage_unit
state
property
Mar. 31, 2017
USD ($)
Dec. 31, 2016
property
Schedule of Equity Method Investments [Line Items]      
Number of self storage properties | property 468    
Total rentable square feet in self storage properties owned by the Joint Venture | ft² 28.5    
Number of storage units owned by the Joint Venture | storage_unit 227    
Number of states that the Joint Venture self storage properties are owned in | state 26    
Contributions to the Joint Venture | $ $ 2,390 $ 0  
Joint Venture | Joint Venture      
Schedule of Equity Method Investments [Line Items]      
Number of self storage properties | property 72   66
Total rentable square feet in self storage properties owned by the Joint Venture | ft² 5.0    
Number of storage units owned by the Joint Venture | storage_unit 40    
Number of states that the Joint Venture self storage properties are owned in | state 13    
Number of self storage properties acquired by the Joint Venture | property 1    
Aggregate purchase price of properties acquired by the Joint Venture | $ $ 9,500    
Contributions to the Joint Venture | $ $ 2,400    
Company's proportionate share of its Joint Venture (percent) 25.00%