Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition (Details)

v3.19.1
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition (Details)
 3 Months Ended 4 Months Ended
Mar. 31, 2019
USD ($)
property
Mar. 31, 2018
USD ($)
Dec. 31, 2016
USD ($)
property
Dec. 31, 2018
USD ($)
Disaggregation of Revenue [Line Items]        
Number of self storage properties | property 706      
Initial term of Joint Venture agreements 4 years      
Performance obligation period of recognition 4 years      
Corporate Joint Venture | 2016 Joint Venture        
Disaggregation of Revenue [Line Items]        
Number of self storage properties | property     66  
Tenant Insurance and Tenant Warranty Protection Plan Revenues        
Disaggregation of Revenue [Line Items]        
Revenue $ 2,100,000 $ 1,700,000    
Retail Products and Supplies        
Disaggregation of Revenue [Line Items]        
Revenue 400,000 400,000    
Property Management, Call Center, and Platform Fees        
Disaggregation of Revenue [Line Items]        
Revenue $ 3,200,000 1,300,000    
Property management fees as percent of monthly gross revenues and net sales revenue of Joint Venture assets 6.00%      
Platform fees per Joint Venture property per month $ 1,250      
Call center fees as percent of monthly gross revenues and net sales revenue of Joint Venture assets 1.00%      
Acquisition Fees        
Disaggregation of Revenue [Line Items]        
Revenue $ 500,000 300,000    
Acquisition fee for the Initial JV Portfolio     $ 4,100,000 $ 4,000,000
Acquisition fees received as a percent of gross capitalization of Initial JV Portfolio     0.65%  
Deferred revenue 4,100,000     $ 4,600,000
Tenant Warranty Protection or Tenant Insurance        
Disaggregation of Revenue [Line Items]        
Revenue $ 1,200,000 $ 500,000    
Percent of total warranty protection plan proceeds received per Joint Venture property (percent) 50.00%