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SUBSEQUENT EVENTS - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jan. 24, 2024 | Jan. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2023 | Dec. 31, 2022 | Feb. 05, 2024 | Feb. 04, 2024 | Oct. 30, 2023 | Oct. 29, 2023 | Mar. 31, 2023
Adviser | David Gladstone |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership percentage by parent |  |  | 100.00% |  | 100.00% |  |  |  |  |  |
Adviser | Gladstone Companies, Inc |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership percentage by parent |  |  | 100.00% |  | 100.00% |  |  |  |  |  |
Gladstone Companies, Ltd. | David Gladstone |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership percentage by parent |  |  | 100.00% |  | 100.00% |  |  |  |  |  |
Gladstone Companies, Inc | Gladstone Companies, Ltd. |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership percentage by parent |  |  | 100.00% |  | 100.00% |  |  |  |  |  |
Credit Facility | Revolving Line of Credit | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment amount |  |  | $ 135,000 |  | $ 135,000 |  |  |  | $ 135,000 | $ 180,000 | $ 180,000
Common Stock ATM Program |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sale of stock, number of shares sold (in shares) |  |  | 1,456,279 | 212,338 | 1,760,449 | 241,978 |  |  |  |  |
Sale of stock, weighted-average gross price per share (in USD per share) |  |  | $ 14.51 | $ 14.11 | $ 14.34 | $ 14.31 |  |  |  |  |
Sale of stock, consideration received |  |  | $ 21,100 | $ 3,000 | $ 25,300 | $ 3,500 |  |  |  |  |
Subsequent Event | Adviser | David Gladstone |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership percentage by parent | 100.00% |  |  |  |  |  |  |  |  |  |
Subsequent Event | Adviser | Voting Trust Board |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Ownership percentage of voting rights | 20.00% |  |  |  |  |  |  |  |  |  |
Effective period after agreement is entered into | 1 year |  |  |  |  |  |  |  |  |  |
Subsequent Event | Credit Facility | Revolving Line of Credit | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment amount |  |  |  |  |  |  | $ 200,000 | $ 135,000 |  |  |
Subsequent Event | Common Stock ATM Program |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Sale of stock, number of shares sold (in shares) |  | 538,206 |  |  |  |  |  |  |  |  |
Sale of stock, weighted-average gross price per share (in USD per share) |  | $ 14.53 |  |  |  |  |  |  |  |  |
Sale of stock, consideration received |  | $ 7,700 |  |  |  |  |  |  |  |  |

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