Annual report pursuant to Section 13 and 15(d)

SUMMMARY OF SIGNIFICANT ACCOUNTING POLICIES\ (Details)

v3.6.0.2
SUMMMARY OF SIGNIFICANT ACCOUNTING POLICIES\ (Details)
 12 Months Ended
Dec. 31, 2016
USD ($)
segment
partnership
property
$ / shares
Dec. 31, 2015
USD ($)
property
$ / shares
Dec. 31, 2014
USD ($)
Property, Plant and Equipment [Line Items]      
Number of self storage properties owned | property 382    
Self storage properties, net $ 1,733,533,000 $ 1,079,101,000  
Fixed rate mortgages held by VIEs 873,194,000 564,886,000  
Intangible asset impairments 0 0 $ 0
Advertising costs 3,100,000 2,400,000 1,700,000
Deferred tax asset 0 0  
Deferred tax liabilities 0 0  
Unrecognized tax benefits $ 0 $ 0  
Common shares of beneficial interest, par value (in dollars per share) | $ / shares $ 0.01 $ 0.01  
Number of reportable segments | segment 1    
Number of properties held for sale | property 2 0  
Goodwill impairment $ 0    
Debt issuance costs, net 3,069,000 $ 1,923,000  
Restricted cash $ 2,767,000 2,712,000  
Building and Improvements [Member] | Minimum [Member]      
Property, Plant and Equipment [Line Items]      
Useful life 7 years    
Building and Improvements [Member] | Maximum [Member]      
Property, Plant and Equipment [Line Items]      
Useful life 40 years    
Furniture and Equipment [Member] | Minimum [Member]      
Property, Plant and Equipment [Line Items]      
Useful life 3 years    
Furniture and Equipment [Member] | Maximum [Member]      
Property, Plant and Equipment [Line Items]      
Useful life 10 years    
Leases, Acquired-in-Place [Member]      
Property, Plant and Equipment [Line Items]      
Customer in-place lease, useful life 12 months    
Customer in-place lease amortization expense $ 12,000,000 12,000,000 $ 8,300,000
Variable Interest Entity, Primary Beneficiary [Member]      
Property, Plant and Equipment [Line Items]      
Number of partnerships considered to be VIEs | partnership 21    
Number of self storage properties owned | property 34    
Self storage properties, net $ 256,800,000 262,600,000  
Mortgages [Member] | Fixed Rate Mortgages [Member]      
Property, Plant and Equipment [Line Items]      
Fixed rate mortgages held by VIEs 201,694,000 176,911,000  
Mortgages [Member] | Fixed Rate Mortgages [Member] | Variable Interest Entity, Primary Beneficiary [Member]      
Property, Plant and Equipment [Line Items]      
Fixed rate mortgages held by VIEs 41,400,000 43,200,000  
Assets [Member] | Accounting Standards Updated 2015-03 [Member]      
Property, Plant and Equipment [Line Items]      
Debt issuance costs, net (5,100,000) (2,800,000)  
Debt Financing [Member] | Accounting Standards Updated 2015-03 [Member]      
Property, Plant and Equipment [Line Items]      
Debt issuance costs, net $ 5,100,000 $ 2,800,000