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Indebtedness - Additional Information (Detail)
Jul. 18, 2019
USD ($)
Property
May 09, 2019
USD ($)
Apr. 30, 2019
USD ($)
Sep. 30, 2019
USD ($)
Dec. 31, 2018
USD ($)
Debt Instrument [Line Items]          
Deferred financing costs       $ 5,686,000 $ 5,927,000
Mortgages-Fixed Rate          
Debt Instrument [Line Items]          
Mortgage loan related to property disposition     $ 18,850,000    
Number Of Property Dispositions | Property 2        
Mortgages-Fixed Rate | Mortgage Property One          
Debt Instrument [Line Items]          
Mortgage loan related to property disposition $ 20,527,000        
Mortgages-Fixed Rate | Mortgage Property Two          
Debt Instrument [Line Items]          
Mortgage loan related to property disposition $ 14,235,000        
Unsecured Revolving Line of Credit          
Debt Instrument [Line Items]          
Credit facility, revolving line of credit   $ 350,000,000      
Maturity date   May 09, 2023      
Maturity term description   option to extend the revolving commitment for two additional 6-month periods under certain circumstances, including the payment of an extension fee      
Deferred financing costs   $ 1,129,000      
Unsecured Revolving Line of Credit | LIBOR          
Debt Instrument [Line Items]          
Debt interest rate   1.55%      
Unsecured Revolving Line of Credit | Minimum | 1-month LIBOR Rate          
Debt Instrument [Line Items]          
Debt interest rate   1.25%      
Unsecured Revolving Line of Credit | Minimum | Base Rate          
Debt Instrument [Line Items]          
Debt interest rate   2.50%      
Unsecured Revolving Line of Credit | Maximum          
Debt Instrument [Line Items]          
Credit facility borrowing capacity   $ 600,000,000      
Unsecured Revolving Line of Credit | Maximum | 1-month LIBOR Rate          
Debt Instrument [Line Items]          
Debt interest rate   2.00%      
Unsecured Revolving Line of Credit | Maximum | Base Rate          
Debt Instrument [Line Items]          
Debt interest rate   1.00%