Quarterly report pursuant to Section 13 or 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 Millions
Sep. 30, 2018
USD ($)
Property
Dec. 31, 2017
USD ($)
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 $ 86.2 $ 85.1
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 $ 13.1 13.3
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 $ 9.2 9.4
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 $ 3.6 3.6
Iskalo Office Holdings, LLC [Member]    
Schedule of Equity Method Investments [Line Items]    
Company common ownership interest 49.00%  
Carrying value of investment $ (0.4) (0.4)
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 $ 4.5 4.1
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 $ 2.8 2.7
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 $ 2.5 2.5
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 $ 11.1 11.5
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 $ 1.3 $ 1.3
NYX Don Mills Storage LP [Member]    
Schedule of Equity Method Investments [Line Items]    
Number of Properties | Property 1  
Company common ownership interest 17.00%  
Carrying value of investment $ 1.0