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Equity and Mezzanine Equity - Additional Information (Detail) - USD ($) $ in Millions | 6 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2022 | Sep. 30, 2021 | Dec. 31, 2021 | Feb. 20, 2020 | Feb. 19, 2020 | Jan. 29, 2020
Class of Stock [Line Items] |  |  |  |  |  |
Temporary equity, contract terms, trigger change in control | 50.00% |  |  |  |  |
Common stock, shares outstanding (in shares) | 39,136,473 |  | 37,473,587 | 60,290,000 | 86,290,000 |
Units held by noncontrolling owners (in shares) | 256,994 | 256,994 |  |  |  |
Gladstone Commercial Limited Partnership |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Company ownership percentage of voting securities | 99.30% |  | 99.30% |  |  |
Number of units redeemed in acquisition (in shares) | 246,039 |  |  |  |  |
Series D Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Temporary equity, contract terms, minimum vote needed to trigger change in control from tender offer | 90.00% |  |  |  |  |
Preferred stock | Series E Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Redeemable preferred stock, dividend rate | 6.625% |  |  |  |  |
Preferred stock | Series G Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Redeemable preferred stock, dividend rate | 6.00% |  |  |  |  |
Preferred stock | Series F Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Redeemable preferred stock, shares issued (in shares) | 126,028 |  |  |  |  |
Consideration received | $ 2.9 |  |  |  |  |
Maximum remaining capacity to sell common stock under open market sale agreement | $ 622.6 |  |  |  |  |
Redeemable preferred stock, shares authorized (in shares) |  |  |  | 26,000,000 |  |
Common Stock ATM Program | Common Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Universal registration statement, amount authorized |  |  |  |  |  | $ 63.0
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) | 1,500,000 |  |  |  |  |
Common Stock ATM Program | Baird, Goldman Sachs, Stifel, and Fifth Third | Common Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Consideration received | $ 31.7 |  |  |  |  |
Maximum remaining capacity to sell common stock under open market sale agreement | 35.5 |  |  |  |  |
2020 Universal Shelf |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Universal registration statement, amount authorized | $ 658.7 |  |  |  |  | 800.0
2020 Universal Shelf | Preferred stock | Series F Preferred Stock |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |
Universal registration statement, amount authorized |  |  |  |  |  | $ 636.5

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