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Related Party Transactions (Narrative) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
item
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Related Party Transaction [Line Items]      
Tenants reinsurance premiums earned by subsidiaries | $ $ 1.5 $ 1.3 $ 1.1
Hughes Family [Member]      
Related Party Transaction [Line Items]      
Percentage ownership of common shares outstanding 14.10%    
Canada [Member] | Hughes Family [Member]      
Related Party Transaction [Line Items]      
Number of self-storage facilities | item 63    
Ownership interest 0.00%