Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 9 Months Ended
Oct. 31, 2017
Jul. 31, 2017
Apr. 30, 2017
Oct. 31, 2016
Jul. 31, 2016
Apr. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Summary Of Significant Accounting Policies [Line Items]                      
Payments to acquire intangible assets                 $ 4,400,000 $ 17,000,000  
Business acquisition, transaction costs             $ 0 $ 1,100,000 500,000 11,800,000  
Impairment losses recognized                 0 0  
Gross amounts of lease intangibles             34,000,000   34,000,000   $ 29,200,000
Accumulated amortization of lease intangibles             27,300,000   27,300,000   16,100,000
Total estimated future amortization expense of intangible assets, year 2017             2,500,000   2,500,000    
Total estimated future amortization expense of intangible assets, year 2018             2,500,000   2,500,000    
Total estimated future amortization expense of intangible assets, year 2019             100,000   100,000    
Total estimated future amortization expense of intangible assets, year 2020             100,000   100,000    
Total estimated future amortization expense of intangible assets, year 2021             100,000   100,000    
Total estimated future amortization expense of intangible assets, thereafter             1,400,000   1,400,000    
Accumulated amortization of debt issuance costs             1,300,000   $ 1,300,000   700,000
Maximum period for reimbursement of offering cost                 60 days    
Maximum offering cost rate                 3.50%    
Reimbursement of offering cost                 $ 0    
Redemptions of common stock                 $ 116    
Minimum percentage of ordinary taxable income to be distributed to stockholders                 90.00%    
Share Redemption Program                      
Summary Of Significant Accounting Policies [Line Items]                      
Redemptions of common stock (in shares)                 160,000    
Redemptions of common stock   $ 460,000 $ 380,000 $ 370,000 $ 160,000 $ 530,000     $ 1,500,000 $ 1,100,000  
Share Redemption Program | Subsequent Event                      
Summary Of Significant Accounting Policies [Line Items]                      
Redemptions of common stock $ 650,000                    
Dealer Manager                      
Summary Of Significant Accounting Policies [Line Items]                      
Underwriting commission                 10.00%    
Maximum dealer manager commission fee percentage of proceeds from Primary Offering                 3.00%    
Class T Common stock | Dealer Manager                      
Summary Of Significant Accounting Policies [Line Items]                      
Monthly stockholder servicing fee accrual description                 accrues daily in an amount equal to 1/365th of 1% of the purchase price per share    
Class T Common stock | Primary Offering Dealer Manager Agreement                      
Summary Of Significant Accounting Policies [Line Items]                      
Percentage of gross proceeds from sale of shares                 10.00%    
Class A Common stock | Primary Offering Dealer Manager Agreement                      
Summary Of Significant Accounting Policies [Line Items]                      
Percentage of gross proceeds from sale of shares                 10.00%    
Non Revolving Debt                      
Summary Of Significant Accounting Policies [Line Items]                      
Accumulated amortization of debt issuance costs             $ 500,000   $ 500,000   $ 200,000
Minimum                      
Summary Of Significant Accounting Policies [Line Items]                      
Estimated useful life                 3 years    
Maximum                      
Summary Of Significant Accounting Policies [Line Items]                      
Estimated useful life                 5 years