| Document and Entity Information | Jul. 11, 2023 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | GLADSTONE INVESTMENT CORPORATION\DE |
| Amendment Flag | false |
| Entity Central Index Key | 0001321741 |
| Document Type | 8-K |
| Document Period End Date | Jul. 11, 2023 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 814-00704 |
| Entity Tax Identification Number | 83-0423116 |
| Entity Address, Address Line One | 1521 Westbranch Drive |
| Entity Address, Address Line Two | Suite 100 |
| Entity Address, City or Town | McLean |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 22102 |
| City Area Code | (703) |
| Local Phone Number | 287-5800 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, $0.001 par value per share |
| Trading Symbol | GAIN |
| Security Exchange Name | NASDAQ |
| A 500 Notes Due 2026 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 5.00% Notes due 2026 |
| Trading Symbol | GAINN |
| Security Exchange Name | NASDAQ |
| M 4.875 Notes Due 20282 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 4.875% Notes due 2028 |
| Trading Symbol | GAINZ |
| Security Exchange Name | NASDAQ |
| M 8.00 Notes Due 20281 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 8.00% Notes due 2028 |
| Trading Symbol | GAINL |
| Security Exchange Name | NASDAQ |
