Quarterly report pursuant to Section 13 or 15(d)

SUBSEQUENT EVENTS (Details)

v3.5.0.2
SUBSEQUENT EVENTS (Details)
$ / shares in Units, storage_unit in Thousands, ft² in Millions
1 Months Ended 3 Months Ended 9 Months Ended
Nov. 01, 2016
USD ($)
Oct. 04, 2016
USD ($)
ft²
storage_unit
state
property
$ / property
Jul. 06, 2016
USD ($)
$ / shares
shares
Nov. 01, 2016
USD ($)
property
shares
Oct. 31, 2016
USD ($)
$ / shares
shares
Sep. 30, 2016
USD ($)
ft²
storage_unit
state
property
Jun. 30, 2016
USD ($)
property
Mar. 31, 2016
USD ($)
property
Sep. 30, 2015
property
Jun. 30, 2015
property
Mar. 31, 2015
property
Sep. 30, 2016
USD ($)
ft²
storage_unit
state
property
shares
Sep. 30, 2015
USD ($)
Oct. 11, 2016
USD ($)
agent
Subsequent Event [Line Items]                            
Number of self storage properties acquired | property           34 25 17 15 21 6 76    
Cash consideration for acquired self storage properties                       $ 323,822,000 $ 132,196,000  
Consideration given, value of OP Equity           $ 4,841,000 $ 80,986,000 $ 19,068,000       $ 104,895,000    
Number of self storage properties | property           352           352    
Total rentable square feet in self storage properties | ft²           21.0           21.0    
Number of storage units | storage_unit           168           168    
Number of states that self storage properties are located in | state           19           19    
Proceeds from issuance of common shares     $ 237,500,000                 $ 238,712,000 $ 278,070,000  
Subsequent Event [Member]                            
Subsequent Event [Line Items]                            
Number of agents used in equity sales agreement | agent                           4
Common shares authorized (in shares)                           $ 200,000,000
Proceeds from issuance of common shares         $ 28,900,000                  
Subsequent Event [Member] | Series of Individually Immaterial Business Acquisitions [Member]                            
Subsequent Event [Line Items]                            
Number of self storage properties acquired | property       2                    
Aggregate purchase price of businesses acquired subsequent to period end   $ 20,000,000   $ 16,900,000                    
Cash consideration for acquired self storage properties       10,600,000                    
Consideration given, value of OP Equity       $ 6,000,000                    
Other working capital liabilities assumed $ 300,000                          
Subsequent Event [Member] | Series of Individually Immaterial Business Acquisitions [Member] | Participating Regional Operator [Member]                            
Subsequent Event [Line Items]                            
Number of self storage properties acquired | property       1                    
Subsequent Event [Member] | Series of Individually Immaterial Business Acquisitions [Member] | Unidentified Third Parties [Member]                            
Subsequent Event [Line Items]                            
Number of self storage properties acquired | property       1                    
OP units [Member] | Subsequent Event [Member] | Series of Individually Immaterial Business Acquisitions [Member]                            
Subsequent Event [Line Items]                            
Number of units issued for acquisitions (in shares) | shares       308,345                    
Due Diligence Costs [Member] | Management [Member] | Subsequent Event [Member] | Participating Regional Operator [Member]                            
Subsequent Event [Line Items]                            
Due diligence expenses payable to the PROs       $ 100,000                    
Joint Venture [Member]                            
Subsequent Event [Line Items]                            
Equity method investments           $ 5,100,000           $ 5,100,000    
Joint Venture [Member] | Subsequent Event [Member]                            
Subsequent Event [Line Items]                            
Equity method investment, monthly property management fee, percent   6.00%                        
Equity method investment, annual call center fee, percent   1.00%                        
Equity method investment, monthly platform fee (in dollars per property) | $ / property   1,250                        
Equity method investment, acquisition fee, percent   0.65%                        
Equity method investment, acquisition fee, annual percentage earned   25.00%                        
Equity method investment, acquisition fee, term   4 years                        
Equity method investment, development management fee, percent   3.00%                        
Equity method investment, warranty protection exchange, proceeds given in exchange, percent   50.00%                        
IStorage Facilities [Member] | Joint Venture [Member] | Subsequent Event [Member]                            
Subsequent Event [Line Items]                            
Aggregate purchase price of JV portfolio   $ 630,000,000                        
Total equity contributed by JV Partners to Joint Venture   320,000,000                        
Equity contributed by JV Partner to Joint Venture   $ 80,000,000                        
Number of self storage properties | property   66                        
Total rentable square feet in self storage properties | ft²   4.5                        
Number of storage units | storage_unit   36                        
Number of states that self storage properties are located in | state   12                        
Equity method investment, ownership percentage   25.00%                        
IStorage Facilities [Member] | Joint Venture [Member] | Subsequent Event [Member] | State Pension Fund [Member]                            
Subsequent Event [Line Items]                            
Equity contributed by JV Partner to Joint Venture   $ 240,000,000                        
Equity method investment, ownership percentage   75.00%                        
Common Shares [Member]                            
Subsequent Event [Line Items]                            
Issuance of common shares (in shares) | shares                       12,046,250    
Common Shares [Member] | Follow On Offering [Member]                            
Subsequent Event [Line Items]                            
Issuance of common shares (in shares) | shares     12,046,250                      
Public offering share price (in dollars per share) | $ / shares     $ 20.75                      
Common Shares [Member] | Follow On Offering [Member] | Subsequent Event [Member]                            
Subsequent Event [Line Items]                            
Issuance of common shares (in shares) | shares         1,500,000                  
Public offering share price (in dollars per share) | $ / shares         $ 19.50