0001321741 2024-09-17 2024-09-17 0001321741 us-gaap:CommonStockMember 2024-09-17 2024-09-17 0001321741 gain:A500NotesDue2026Member 2024-09-17 2024-09-17 0001321741 gain:M4.875NotesDue20282Member 2024-09-17 2024-09-17 0001321741 gain:M8.00NotesDue20281Member 2024-09-17 2024-09-17 GLADSTONE INVESTMENT CORPORATION\DE false 0001321741 8-K 2024-09-17 DE 814-00704 83-0423116 1521 Westbranch Drive Suite 100 McLean VA 22102 (703) 287-5800 false false false false Common Stock, $0.001 par value per share GAIN NASDAQ 5.00% Notes due 2026 GAINN NASDAQ 4.875% Notes due 2028 GAINZ NASDAQ 8.00% Notes due 2028 GAINL NASDAQ false