Quarterly report pursuant to Section 13 or 15(d)

SUBSEQUENT EVENTS (Details)

v3.10.0.1
SUBSEQUENT EVENTS (Details)
$ / shares in Units, unit in Thousands, storage_unit in Thousands, $ in Thousands, ft² in Millions
 1 Months Ended 3 Months Ended 6 Months Ended
Jul. 13, 2018
USD ($)
$ / shares
shares
Aug. 06, 2018
USD ($)
Sep. 30, 2018
USD ($)
ft²
state
property
unit
lender
$ / property
Jun. 30, 2018
USD ($)
ft²
storage_unit
state
property
Jun. 30, 2017
USD ($)
Oct. 01, 2018
ft²
property
unit
Subsequent Event [Line Items]            
Number of self storage properties | property       551    
Total rentable square feet in self storage properties owned by the Joint Venture | ft²       34.0    
Number of storage units owned by the Joint Venture | storage_unit       270    
Number of states in which self storage properties are owned and operated | state       29    
Contributions to the 2018 Joint Venture by Company for Acquisition Deposit       $ 2,390 $ 12,647  
Subsequent Event            
Subsequent Event [Line Items]            
Common share offering, number of shares issued | shares 5,900,000          
Common share offering, price per share (in dollars per share) | $ / shares $ 29.86          
Common share offering, net proceeds $ 175,700          
2018 Joint Venture | Subsequent Event            
Subsequent Event [Line Items]            
Joint venture total cash deposit for Acquisition   $ 53,000        
2018 Joint Venture | Forecast | Subsequent Event            
Subsequent Event [Line Items]            
Aggregate purchase of 2018 Joint Venture Acquisition     $ 1,325,000      
Number of self storage properties | property     112     105
Total rentable square feet in self storage properties owned by the Joint Venture | ft²     8.7     8.1
Number of storage units owned by the Joint Venture | unit     68     63
Number of states in which self storage properties are owned and operated | state     17      
Joint venture, estimated transaction expenses     $ 19,000      
NSA Member | 2018 Joint Venture | Subsequent Event            
Subsequent Event [Line Items]            
Contributions to the 2018 Joint Venture by Company for Acquisition Deposit   $ 34,100        
NSA Member | 2018 Joint Venture | Forecast | Subsequent Event            
Subsequent Event [Line Items]            
Commitment of Company to 2018 Joint Venture     $ 160,800      
Company's proportionate share of its Joint Venture (percent)     25.00%      
Joint venture, estimated capital expenditures     $ 6,000      
Joint venture, Company's additional commitment for Distribution Properties     $ 64,000      
Joint venture, additional commitment, number of Distribution Properties | property     6      
Joint venture, monthly property management fee percent     6.00%      
Joint venture, monthly platform fee amount | $ / property     1,250      
Joint venture, acquisition fee     $ 4,000      
Joint venture, acquisition fee term     4 years      
Joint venture, development management fee amount     3.00%      
Joint venture, reimbursement of integration and transfer of properties     $ 2,000      
Joint venture, warranty protection proceeds percent     50.00%      
JV Investor | 2018 Joint Venture | Forecast | Subsequent Event            
Subsequent Event [Line Items]            
Joint venture commitment of partner     $ 482,300      
Joint venture, ownership percentage of partner     75.00%      
2018 Joint Venture | Forecast | Subsequent Event            
Subsequent Event [Line Items]            
Number of lenders for 2018 Joint Venture financing | lender     2      
Face amount of 2018 Joint Venture debt     $ 643,000      
Interest rate stated percentage of 2018 Joint Venture debt     4.34%      
Term of 2018 Joint Venture debt     10 years