Annual report pursuant to Section 13 and 15(d)

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

v3.19.3.a.u2
Organization, Basis of Presentation and Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2019
USD ($)
subsidiary
shares
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Jan. 01, 2019
USD ($)
agreement
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 below-market lease 2,500,000 $ 2,000,000 $ 1,500,000  
Total amortization expense related to intangible assets $ 19,200,000 17,700,000 15,900,000  
Maturity period of highly-liquid investments at the time of purchase three months or less      
Payments of deferred financing costs $ (2,480,000) (386,000) (1,990,000)  
Total amortization expense related to deferred financing costs is included in interest expense $ 1,641,000 1,445,000 1,713,000  
Aggregate Deferred Rent Write Off   200,000 0  
Uncertain tax positions percentage 50.00%      
Uncertain tax positions $ 0 0 0  
ARO liabilities accrued in connection with acquisitions 164,000 0 0  
Expenses recorded to general and administrative expense 100,000 100,000 100,000  
Aggregate undiscounted obligation on properties 6,200,000      
Right-of-use assets from operating leases 5,794,000      
Number of operating ground lease arrangements | agreement       4
Above Market Leases        
Organization And Significant Accounting Policies [Line Items]        
Amortization related to above-market lease $ 1,100,000      
Amortization related to above-market lease   $ 1,100,000 $ 700,000  
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% 97.50%    
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      
ASU 2016-02        
Organization And Significant Accounting Policies [Line Items]        
Right-of-use assets from operating leases       $ 6,000,000
Weighted average discount rate (percent)       5.34%
Number of fixed rental charges operating ground lease arrangements | agreement       3
Number of variable charges operating ground lease arrangements | agreement       1
Number of options to extend operating ground lease arrangements | agreement       3
Number of early termination options operating ground lease arrangements | agreement       1
ASU 2016-02 | Minimum        
Organization And Significant Accounting Policies [Line Items]        
Discount rate, basis spread on variable rate (percent)       2.50%
ASU 2016-02 | Maximum        
Organization And Significant Accounting Policies [Line Items]        
Discount rate, basis spread on variable rate (percent)       2.60%