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Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2024
Mar. 04, 2025
Jun. 30, 2024
Document Information [Line Items]      
Entity Central Index Key 0001487428    
Entity Registrant Name Horizon Technology Finance Corp    
Amendment Flag false    
Current Fiscal Year End Date --12-31    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2024    
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2024    
Document Transition Report false    
Entity File Number 814-00802    
Entity Incorporation, State or Country Code DE    
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    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 428,200,000
Entity Common Stock, Shares Outstanding   40,315,008  
Auditor Firm ID 49    
Auditor Name RSM US LLP    
Auditor Location Hartford, Connecticut    
The 6.25% Notes due 2027 [Member]      
Document Information [Line Items]      
Title of 12(b) Security 6.25% Notes due 2027    
Trading Symbol HTFC    
Security Exchange Name NYSE    
The 4.875% Notes due 2026 [Member]      
Document Information [Line Items]      
Title of 12(b) Security 4.875% Notes due 2026    
Trading Symbol HTFB    
Security Exchange Name NYSE    
Common Stock [Member]      
Document Information [Line Items]      
Title of 12(b) Security Common Stock, par value $0.001 per share    
Trading Symbol HRZN    
Security Exchange Name NASDAQ