Annual report pursuant to Section 13 and 15(d)

Organization, Basis of Presentation and Significant Accounting Policies - Additional Information (Detail)

v3.20.4
Organization, Basis of Presentation and Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2020
USD ($)
segment
tenant
subsidiary
shares
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Organization And Significant Accounting Policies [Line Items]      
Number of subsidiaries interest owned in general and limited partnership | subsidiary 2    
Non-qualifying income related to real estate portfolio $ 0    
Amortization related to above-market lease 52,000 $ 53,000 $ 0
Amortization related to below-market lease 2,800,000 2,500,000 2,000,000.0
Total amortization expense related to intangible assets $ 19,400,000 19,200,000 17,700,000
Maturity period of highly-liquid investments at the time of purchase three months or less    
Payments of deferred financing costs $ (606,000) (2,480,000) (386,000)
Total amortization expense related to deferred financing costs is included in interest expense 1,531,000 1,641,000 1,445,000
Deferred rent write-offs $ 200,000 0  
Uncertain tax positions percentage 50.00%    
Uncertain tax positions $ 0 0 0
ARO liabilities accrued in connection with acquisitions 0 164,000 0
Expenses recorded to general and administrative expense 100,000 100,000 100,000
Aggregate undiscounted obligation on properties $ 5,600,000    
Number of reporting segments | segment 1    
Number of operating segments | segment 1    
Rent obligations deferred, number of tenants | tenant 3    
Rent obligations deferred, percentage 2.00%    
Above Market Leases      
Organization And Significant Accounting Policies [Line Items]      
Amortization related to above-market lease $ 800,000 $ 1,100,000  
Amortization related to above-market lease     $ 1,100,000
Minimum      
Organization And Significant Accounting Policies [Line Items]      
Expected lease up period for estimating carrying costs 9 months    
Remaining term of in-place leases and unamortized lease 7 years    
REIT taxable income to its stockholders (as percent) 90.00%    
Percentage of discount rate for calculating undiscounted obligation (as percent) 2.50%    
Maximum      
Organization And Significant Accounting Policies [Line Items]      
Expected lease up period for estimating carrying costs 18 months    
Remaining term of in-place leases and unamortized lease 15 years    
REIT taxable income to its stockholders (as percent) 100.00%    
Percentage of discount rate for calculating undiscounted obligation (as percent) 7.00%    
Building and Improvements      
Organization And Significant Accounting Policies [Line Items]      
Estimated useful life 39 years    
Equipment and Fixtures | Minimum      
Organization And Significant Accounting Policies [Line Items]      
Estimated useful life 5 years    
Equipment and Fixtures | Maximum      
Organization And Significant Accounting Policies [Line Items]      
Estimated useful life 20 years    
GCLP Business Trust I      
Organization And Significant Accounting Policies [Line Items]      
Subsidiary and business trust of the Company, formed under the laws of the Commonwealth of Massachusetts, date Dec. 28, 2005    
Percentage of limited partnership interest transferred to business unit (as percent) 99.00%    
Number of trust shares exchanged for limited partnership interest (in shares) | shares 100    
Operating Partnership      
Organization And Significant Accounting Policies [Line Items]      
Company ownership percentage of voting securities 98.60% 98.60%  
Gladstone Commercial Advisers, Inc.      
Organization And Significant Accounting Policies [Line Items]      
Company ownership percentage of voting securities 100.00%    
GCLP Business Trust II      
Organization And Significant Accounting Policies [Line Items]      
Percentage of limited partnership interest transferred to business unit (as percent) 1.00%    
Number of trust shares exchanged for general partnership interest (in shares) | shares 100