Quarterly report pursuant to Section 13 or 15(d)

Investment in Joint Ventures - Summary of Company's Unconsolidated Joint Ventures (Parenthetical) (Detail)

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Investment in Joint Ventures - Summary of Company's Unconsolidated Joint Ventures (Parenthetical) (Detail)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2018
USD ($)
Property
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Property
Schedule of Equity Method Investments [Line Items]      
Number of storage facilities acquired | Property 2    
Payment for property acquisition $ 19,409 $ 9,576  
Mortgages payable 12,397   $ 12,674
Distributions from unconsolidated joint ventures 6,276 5,071  
Payment for property acquisition 19,487    
Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Contribution of company to joint venture as share in capital 2,900    
Distributions from unconsolidated joint ventures 4,200    
Excess of investment over net asset due to capitalization of acquisition related costs 1,700    
Sovran HHF Storage Holdings II LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Distributions from unconsolidated joint ventures 1,500    
191 III Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Contribution of company to joint venture as share in capital 100    
Distributions from unconsolidated joint ventures 300    
Life Storage-SERS Storage LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Distributions from unconsolidated joint ventures 100    
Iskalo Office Holdings, LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Distributions from unconsolidated joint ventures 200    
Rent paid during the period 900 $ 900  
Urban Box Coralway Storage, LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Contribution of company to joint venture as share in capital 500    
SNL/Orix 1200 McDonald Ave., LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Contribution of company to joint venture as share in capital 100    
Non-recourse mortgage loan principal outstanding 11,100    
SNL Orix Merrick, LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Contribution of company to joint venture as share in capital 100    
Non-recourse mortgage loan principal outstanding 12,100    
Review Avenue Partners LLC [Member] | Common Stock Shares [Member]      
Schedule of Equity Method Investments [Line Items]      
Contribution of company to joint venture as share in capital 300    
NYX Don Mills Storage LP [Member] | Common Stock Shares [Member]      
Schedule of Equity Method Investments [Line Items]      
Contribution of company to joint venture as share in capital $ 1,000    
Arizona [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 11    
Arizona [Member] | N 32nd Street Self Storage, LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 1    
Colorado [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 4    
Florida [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 3    
Florida [Member] | Urban Box Coralway Storage, LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 1    
Georgia [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 1    
Georgia [Member] | Life Storage-SERS Storage LLC [Member] | Additional Storage Facilities [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of storage facilities acquired | Property 3   3
Mortgages payable     $ 22,000
Payment for property acquisition     $ 39,100
Kentucky [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 2    
Nevada [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 5    
New Jersey [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 2    
New Jersey [Member] | Sovran HHF Storage Holdings II LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 17    
Ohio [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 6    
Pennsylvania [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 1    
Pennsylvania [Member] | Sovran HHF Storage Holdings II LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 3    
Tennessee [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 2    
Texas [Member] | Sovran HHF Storage Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 20    
Texas [Member] | Sovran HHF Storage Holdings II LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 10    
Arizona, Nevada and Tennessee [Member] | Sovran HHF Storage Holdings LLC [Member] | Storage Facilities [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of storage facilities acquired | Property     18
Payment for property acquisition     $ 330,000
Mortgages payable     $ 135,000
Number of properties collateral for debt | Property     16
California [Member] | 191 III Holdings LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 6    
California [Member] | 191 III Holdings LLC [Member] | Six Storage Facilities [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of storage facilities acquired | Property     6
Mortgages payable     $ 57,200
Payment for property acquisition     $ 104,100
New York [Member] | SNL/Orix 1200 McDonald Ave., LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 1    
New York [Member] | SNL Orix Merrick, LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 1    
New York [Member] | Review Avenue Partners LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Number of self-storage facilities | Property 1