Annual report pursuant to Section 13 and 15(d)

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

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Investment in Joint Ventures - Summary of Company's Unconsolidated Joint Ventures (Detail)
$ in Thousands
Dec. 31, 2017
USD ($)
Property
Dec. 31, 2016
USD ($)
Schedule of Equity Method Investments [Line Items]    
Carrying value of investment $ 133,458 $ 67,300
Sovran HHF Storage Holdings LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 57  
Company common ownership interest 20.00%  
Carrying value of investment $ 85,100 43,800
Sovran HHF Storage Holdings II LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 30  
Company common ownership interest 15.00%  
Carrying value of investment $ 13,300 13,500
191 III Holdings LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 6  
Company common ownership interest 20.00%  
Carrying value of investment $ 9,400 700
Life Storage-SERS Storage LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 3  
Company common ownership interest 20.00%  
Carrying value of investment $ 3,600  
Iskalo Office Holdings, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Company common ownership interest 49.00%  
Carrying value of investment $ (400) (400)
Urban Box Coralway Storage, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 1  
Company common ownership interest 85.00%  
Carrying value of investment $ 4,100 4,100
SNL/Orix 1200 McDonald Ave., LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 1  
Company common ownership interest 5.00%  
Carrying value of investment $ 2,700 2,700
SNL Orix Merrick, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 1  
Company common ownership interest 5.00%  
Carrying value of investment $ 2,500 $ 2,500
Review Avenue Partners LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 1  
Company common ownership interest 40.00%  
Carrying value of investment $ 11,500  
N 32nd Street Self Storage, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 1  
Company common ownership interest 46.00%  
Carrying value of investment $ 1,300