Note 8 - Federal Income Tax - Tax Characters of Distributions Paid (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Ordinary income	$ 55,984	$ 49,467	$ 42,576
Total	$ 55,984	$ 49,467	$ 42,576

Amount of dividend distribution from ordinary income and capital gain paid during the period. Excludes distribution for tax return of capital.

No definition available.

Name:	hrzn_InvestmentCompanyDividendDistributionPaid
Namespace Prefix:	hrzn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration