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Indebtedness - Additional Information (Detail)
1 Months Ended 3 Months Ended 6 Months Ended
May 01, 2017
USD ($)
Jun. 30, 2017
USD ($)
Property
May 31, 2017
USD ($)
Feb. 28, 2017
USD ($)
Jun. 30, 2017
USD ($)
Property
Jun. 30, 2016
USD ($)
Jun. 30, 2017
USD ($)
Property
Jun. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Debt Instrument [Line Items]                  
Loss on extinguishment of debt $ (572,000)       $ (572,000) $ (558,000) $ (572,000) $ (558,000)  
Proceeds from credit facility   $ 31,250,000 $ 9,000,000       $ 63,190,000 $ 93,501,000  
Number of property dispositions | Property   3     3   3    
Defeasance mortgage loan related to property disposition         $ 20,586,000        
Secured Credit Facility                  
Debt Instrument [Line Items]                  
Proceeds from credit facility       $ 22,000,000          
Unsecured credit facility   $ 300,000,000     $ 300,000,000   $ 300,000,000   $ 312,500,000
Maturity date Sep. 17, 2018                
Unsecured Credit Facility                  
Debt Instrument [Line Items]                  
Unsecured credit facility $ 300,000,000                
Term Loan                  
Debt Instrument [Line Items]                  
Unsecured credit facility $ 50,000,000                
Maturity date May 01, 2022                
Term Loan | LIBOR                  
Debt Instrument [Line Items]                  
Debt interest rate 1.45%                
Revolving Commitment                  
Debt Instrument [Line Items]                  
Unsecured credit facility $ 250,000,000                
Maturity date May 01, 2021                
Revolving Commitment | LIBOR                  
Debt Instrument [Line Items]                  
Debt interest rate 1.50%