Annual report pursuant to Section 13 and 15(d)

Mortgage Notes Payable, Revolving Credit Facility, and Term Loan Facility - Additional Information (Detail)

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Mortgage Notes Payable, Revolving Credit Facility, and Term Loan Facility - Additional Information (Detail)
 12 Months Ended
Oct. 27, 2017
USD ($)
Oct. 05, 2015
USD ($)
Dec. 31, 2018
USD ($)
property
mortgage
Dec. 31, 2017
USD ($)
Aug. 31, 2013
USD ($)
Debt Instrument [Line Items]          
Number of properties collateralized in mortgage notes payable | property     100    
Net book value of collateralized mortgage properties     $ 5,900,000    
Fair value of mortgage notes payable outstanding     444,200,000    
Long-term debt     566,059,000 $ 542,627,000  
Line of credit facility, maximum borrowing capacity     75,000,000.0   $ 25,000,000.0
Borrowings under revolving credit facility, net     $ 50,084,000 20,715,000  
Line of credit at an interest rate (as percent)     4.24%    
Weighted average interest rate on debt outstanding (as percent)     4.59%    
Mortgage notes payable          
Debt Instrument [Line Items]          
Number of mortgage notes payable | mortgage     47    
Number of properties collateralized in mortgage notes payable | property     68    
Net book value of collateralized mortgage properties     $ 643,300,000    
Collateral     $ 10,200,000    
Collateral (as percent)     2.30%    
Number of mortgages repaid | mortgage     2    
Number of properties collateralized | property     2    
Number of long-term mortgages issued | property     3    
Number of properties to issue collateralized mortgage notes payable | property     3    
Number of long-term mortgages maturity extended | property     4    
Number of properties maturity extended collateralized mortgage notes payable | property     9    
Long-term debt     $ 441,346,000 $ 447,380,000  
Weighted average interest rate on debt outstanding (as percent)     4.69%    
LIBOR          
Debt Instrument [Line Items]          
Spread on LIBOR (as percent) 2.75%        
Five year term loan facility          
Debt Instrument [Line Items]          
Debt instrument term 5 years        
Revolving credit facility          
Debt Instrument [Line Items]          
Debt instrument term 4 years        
Line of credit          
Debt Instrument [Line Items]          
Line of credit facility, maximum borrowing capacity   $ 85,000,000.0      
Debt instrument, fee $ 900,000        
Borrowings under revolving credit facility, net     $ 125,600,000    
Letters of credit, outstanding     2,100,000    
Line of credit facility, maximum additional amount drawn     $ 32,400,000    
Line of credit | Five year term loan facility          
Debt Instrument [Line Items]          
Line of credit facility, maximum borrowing capacity   $ 25,000,000.0      
Debt instrument term   5 years      
Letter of credit          
Debt Instrument [Line Items]          
Weighted average interest rate on debt outstanding (as percent)     1.75%