Quarterly report pursuant to Section 13 or 15(d)

SUBSEQUENT EVENTS (Details)

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SUBSEQUENT EVENTS (Details) - property
Oct. 31, 2018
Sep. 30, 2018
Subsequent Event [Line Items]    
Number of self storage properties   668
Subsequent Event | Puerto Rico    
Subsequent Event [Line Items]    
Number of self storage properties 6  
Subsequent Event | Louisiana    
Subsequent Event [Line Items]    
Number of self storage properties under contract to be acquired 11  
Subsequent Event | Southern Self Storage, LLC    
Subsequent Event [Line Items]    
Number of self storage properties 9  
Number of self storage properties to be contributed to Company per definitive agreement 6  
Number of self storage properties in initial PRO portfolio 23