| Document And Entity Information | May 25, 2023 |
| Document Information [Line Items] | |
| Entity, Registrant Name | HORIZON TECHNOLOGY FINANCE CORPORATION |
| Document, Type | 8-K |
| Document, Period End Date | May 25, 2023 |
| Entity, Incorporation, State or Country Code | DE |
| Entity, File Number | 814-00802 |
| Entity, Tax Identification Number | 27-2114934 |
| Entity, Address, Address Line One | 312 Farmington Avenue |
| Entity, Address, City or Town | Farmington |
| Entity, Address, State or Province | CT |
| Entity, Address, Postal Zip Code | 06032 |
| City Area Code | 860 |
| Local Phone Number | 676-8654 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0001487428 |
| CommonStock Custom [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | HRZN |
| Security Exchange Name | NASDAQ |
| NotesDue20264875 Custom [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 4.875% Notes due 2026 |
| Trading Symbol | HTFB |
| Security Exchange Name | NYSE |
| NotesDue2027625 Custom [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 6.25% Notes due 2027 |
| Trading Symbol | HTFC |
| Security Exchange Name | NYSE |
