Quarterly report pursuant to Section 13 or 15(d)

Equity and Mezzanine Equity - Additional Information (Detail)

v3.21.2
Equity and Mezzanine Equity - Additional Information (Detail) - USD ($)
 3 Months Ended 9 Months Ended 12 Months Ended
Jun. 30, 2021
Jun. 28, 2021
Jun. 23, 2021
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Aug. 05, 2021
Feb. 20, 2020
Feb. 19, 2020
Jan. 29, 2020
Jan. 11, 2019
Class of Stock [Line Items]                          
Temporary equity, contract terms, trigger change in control           50.00%              
Series D preferred stock offering costs write off       $ 0 $ 0 $ 2,141,000 $ 0            
Common stock, shares authorized (in shares)       62,290,000   62,290,000   60,290,000          
Common stock, shares outstanding (in shares)       36,880,119   36,880,119   35,331,970   60,290,000 86,290,000    
Units held by noncontrolling owners (in shares)           256,994   503,033          
Gladstone Commercial Limited Partnership                          
Class of Stock [Line Items]                          
Company ownership percentage of voting securities       99.30%   99.30%   98.60%          
Number of units redeemed in acquisition (in shares)           246,039              
Series G Preferred Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, dividend rate percentage     6.00%                    
Redeemable preferred stock, shares authorized (in shares)     4,000,000                    
Series D Preferred Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, dividend rate percentage   7.00%                      
Temporary equity, contract terms, minimum vote needed to trigger change in control from tender offer (as percent)       90.00%   90.00%              
Shares redeemed (in shares) 3,509,555                        
Redemption price (in usd per share)       $ 25.1458333   $ 25.1458333              
Aggregate redemption price $ 88,300,000                        
Series D preferred stock offering costs write off $ 2,100,000                        
Series F Preferred Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, shares authorized (in shares)       26,000,000   26,000,000   26,000,000          
Common Stock                          
Class of Stock [Line Items]                          
Common stock, shares authorized (in shares)                 62,290,000        
Common Stock | Senior Common Stock                          
Class of Stock [Line Items]                          
Common stock, shares authorized (in shares)                 950,000        
Preferred Stock | Series G Preferred Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, shares authorized (in shares)                 4,000,000        
Preferred Stock | Series D Preferred Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, shares authorized (in shares)                 2,490,445        
Preferred Stock | Series E Preferred Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, dividend rate percentage           6.625%              
Redeemable preferred stock, shares authorized (in shares)                 6,760,000        
Preferred Stock | Series F Preferred Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, shares issued (in shares)           217,422              
Consideration received           $ 4,900,000              
Maximum remaining capacity to sell common stock under open market sale agreement       $ 628,200,000   628,200,000              
Redeemable preferred stock, shares authorized (in shares)                 26,000,000 26,000,000      
Baird, Goldman Sachs, Stifel, Fifth Third, and U.S. Bancorp Investments, Inc. | Preferred Stock | Series E Preferred Stock                          
Class of Stock [Line Items]                          
Maximum aggregate sales price of shares to be issued under open market sale agreement       100,000,000   100,000,000              
Maximum remaining capacity to sell common stock under open market sale agreement       92,800,000   $ 92,800,000              
Common Stock ATM Program | Baird, Goldman Sachs, Stifel, Fifth Third, and U.S. Bancorp Investments, Inc. | Common Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, shares issued (in shares)           1,200,000              
Consideration received           $ 24,100,000              
Maximum aggregate sales price of shares to be issued under open market sale agreement       250,000,000   250,000,000              
Maximum remaining capacity to sell common stock under open market sale agreement       159,400,000   159,400,000              
2019 Universal Shelf                          
Class of Stock [Line Items]                          
Universal registration statement, amount authorized       352,700,000   352,700,000             $ 500,000,000
2020 Universal Shelf                          
Class of Stock [Line Items]                          
Universal registration statement, amount authorized       $ 691,700,000   $ 691,700,000           $ 800,000,000  
2020 Universal Shelf | Preferred Stock | Series F Preferred Stock                          
Class of Stock [Line Items]                          
Universal registration statement, amount authorized                       $ 636,500,000  
Over-Allotment Option | Redeemable Preferred Stock                          
Class of Stock [Line Items]                          
Redeemable preferred stock, shares issued (in shares)   4,000,000                      
Public offering price (in usd per share)   $ 25.00                      
Consideration received   $ 100,000,000                      
Gross proceeds of the offering   $ 96,600,000