Quarterly report pursuant to Section 13 or 15(d)

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition (Details)

v3.19.3
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Revenue Recognition (Details)
 3 Months Ended 9 Months Ended
Sep. 30, 2019
USD ($)
property
Dec. 31, 2018
USD ($)
Sep. 30, 2018
USD ($)
Dec. 31, 2016
USD ($)
property
Sep. 30, 2019
USD ($)
property
Sep. 30, 2018
USD ($)
Disaggregation of Revenue [Line Items]            
Number of self storage properties | property 735       735  
Initial term of unconsolidated real estate 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 $ 2,400,000   $ 2,000,000.0   $ 6,700,000 $ 5,500,000
Retail Products and Supplies            
Disaggregation of Revenue [Line Items]            
Revenue 400,000   300,000   1,300,000 1,100,000
Property Management, Call Center, and Platform Fees            
Disaggregation of Revenue [Line Items]            
Revenue 3,300,000   1,900,000   $ 9,700,000 4,600,000
Property management fees as percent of monthly gross revenues and net sales revenue of unconsolidated real estate venture assets         6.00%  
Platform fees per unconsolidated real estate venture property per month         $ 1,250  
Call center fees as percent of monthly gross revenues and net sales revenue of unconsolidated real estate venture assets         1.00%  
Acquisition Fees            
Disaggregation of Revenue [Line Items]            
Revenue 400,000   500,000   $ 1,400,000 1,100,000
Acquisition fee   $ 4,000,000.0   $ 4,100,000    
Acquisition fees received as a percent of gross capitalization of Initial 2016 JV Portfolio       0.65%    
Deferred revenue related to acquisition fees 3,200,000 $ 4,600,000     3,200,000  
Tenant Warranty Protection or Tenant Insurance            
Disaggregation of Revenue [Line Items]            
Revenue $ 1,200,000   $ 700,000   $ 3,600,000 $ 1,700,000
Percent of total warranty protection plan proceeds received per unconsolidated real estate venture property (percent)         50.00%