Document And Entity Information
Statistical Measurement [Axis]
Note To Financial Statement Details Textual
Significant Accounting Policies
Investment, Policy [Policy Text Block]
Consolidated Schedule of Investments (Unaudited)
ecd_NonRule10b51ArrTrmntdFlag
Non-Rule 10b5-1 Arrangement Terminated [Flag]
Note 3 - Related Party Transactions
hrzn_IncreaseDecreaseInEndoftermPayments
(Increase) decrease in end-of-term payments
Amount of increase (decrease) in end-of-term payments.
ecd_NonRule10b51ArrAdoptedFlag
Non-Rule 10b5-1 Arrangement Adopted [Flag]
Note 4 - Investments
hrzn_IncreaseDecreaseInUnearnedIncome
Decrease in unearned income
Amount of increase (decrease) in unearned income.
Trading Arrangements, by Individual [Table]
Note 5 - Transactions With Affiliated Companies
Warrant investments received and recorded as unearned income
Amount of warrant investments received and recorded as unearned income.
Material Terms of Trading Arrangement [Text Block]
Note 6 - Fair Value
End-of-term payments receivable
Amount of end-of-term payments receivable in noncash or part noncash transaction.
Note 7 - Borrowings
Financial Instrument [Axis]
us-gaap_InvestmentCompanyContractualAndVoluntaryFeesWaived
Investment Company, Contractual and Voluntary Fees Waived
Note 8 - Financial Instruments With Off-balance-sheet Risk
Note 10 - Distributions
Alternative Energy [Member]
Note 11 - Earnings Per Share
Net decrease in net assets resulting from operations per common share - basic (in dollars per share)
Minimum [Member]
Note 12 - Financial Highlights
Consolidated Schedule of Investments - Investments (Unaudited) (Details)
Statistical Measurement [Domain]
Dividends Payable [Table]
Consolidated Schedule of Investments - Investments (Unaudited) 2 (Details)
Maximum [Member]
us-gaap_SharePrice
Share Price (in dollars per share)
Per share market value, beginning of period (in dollars per share)
Per share market value, end of period (in dollars per share)
Consolidated Schedule of Investments - Investments (Unaudited) (Details) (Parentheticals)
Note 3 - Related Party Transactions - Expiration Dates of Contingent Future Liability (Details)
Note 4 - Investments - Investments (Details)
Note 4 - Investments - Schedule of Summarized Financial Information (Details)
Note 5 - Transactions With Affiliated Companies - Schedule of Investments in Affiliated Companies (Details)
March 31, 2027 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
Note 5 - Transactions With Affiliated Companies - Schedule of Investments in Affiliated Companies 2 (Details)
NAV %
Note 6 - Fair Value - Assets at Fair Value on a Recurring Basis (Details)
Schedule of Investments [Table]
Note 6 - Fair Value - Significant Level 3 Fair Value Measurement Inputs (Details)
Note 6 - Fair Value - Reconciliation of Level 3 Assets Measured on a Recurring Basis (Details)
Note 7 - Borrowings - Borrowings (Details)
Distributions payable
Note 8 - Financial Instruments With Off-balance-sheet Risk - Unfunded Commitments (Details)
Note 10 - Distributions - Distribution Activity (Details)
Note 11 - Earnings Per Share - Schedule of Earnings Per share (Details)
Basis of Presentation and Significant Accounting Policies [Text Block]
Note 12 - Financial Highlights - Financial Highlights (Details)
Notes To Financial Statements
Notes To Financial Statements [Abstract]
hrzn_InvestmentsFairValueNonaccrualStatus
Investments, Fair Value, Nonaccrual Status
The fair value of investments on nonaccrual status.
Payment-in-kind (“PIK”) interest income
Interest Income, Operating, Paid in Kind
PIK interest on investments
us-gaap_IncentiveFeePayable
Incentive Fee Payable
us-gaap_InvestmentCompanyIncentiveFeeWaived
Investment Company, Incentive Fee Waived
hrzn_InvestmentsCostNonaccrualStatus
Investments, Cost, Nonaccrual Status
The cost value of investments on nonaccrual status.
hrzn_InvestmentNonaccrualIncomeNotReceivedInCashPercent
Investment, Nonaccrual, Income Not Received in Cash, Percent
The percent of nonaccrual investment income not received in cash.
us-gaap_InvestmentIncomeOperatingAfterExpenseAndTax
Net investment income
Net investment income
One Investment [Member]
Related to one investment.
June 30, 2027 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
Provision for excise tax
Net realized gain on investments
us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingAfterTax
GT Medical Technologies, Inc. [Member]
Represents GT Medical Technologies, Inc.
Investments in money market funds acquired in Merger
Amount of investments in money market funds acquired in Merger.
Dividends, cash
June 30, 2026 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
Dividends, stock
Increase (decrease) in base management fee payable
Financial Instruments [Domain]
us-gaap_PaymentsForPurchaseOfInvestmentOperatingActivity
Investment in RoHo Joint Venture
Distributions declared per share (in dollars per share)
Monroe Capital Intermediate Holdings, LLC [Member]
Pertains to the related parties.
hrzn_OwnershipPercentageAcquired
Ownership Percentage
Pertains to the percentage of ownership acquired.
Zero Investments [Member]
Represents zero investments.
Weighted Average [Member]
us-gaap_IncreaseDecreaseInAccruedInterestReceivableNet
Decrease in interest receivable
Investment Company, Nonconsolidated Subsidiary [Table]
Equity Purchase Agreement [Member]
Pertains to the type of arrangement.
Investment Company, Nonconsolidated Subsidiary, Summarized Financial Information [Table Text Block]
us-gaap_SharesOutstanding
Balance (in shares)
Balance (in shares)
Multiple Probability Weighted Scenario Model [Member]
Related to Multiple Probability Weighted Scenario Model.
Dividends [Axis]
Dividends [Domain]
Decrease in other accrued expenses
Adjustments to reconcile net decrease in net assets resulting from operations to net cash provided by operating activities:
Preferred stock, par value $0.001 per share, 1,000,000 shares authorized, zero shares issued and outstanding as of June 30, 2026 and December 31, 2025
us-gaap_Liabilities
Total liabilities
Liabilities
us-gaap_LiabilitiesAndStockholdersEquity
Total liabilities and members’ capital
Selected Interest Rates (Daily) [Member]
Represents the Selected Interest Rates (Daily).
InfoBionic, Inc [Member]
Represents InfoBionic, Inc.
hrzn_FederalExciseTaxPercent
Federal Excise Tax, Percent
The federal excise tax percent.
Fee income
hrzn_DebtInstrumentBasisSpreadOnVariableRateTreasuryYieldMaturity
Debt Instrument, Basis Spread on Variable Rate, Treasury Yield Maturity (Year)
Period of maturity for treasury yield used to calculate basis spread on variable rate of debt instrument.
Subsequent Event [Member]
Nuveen Facility [Member]
Represents the Nuveen Facility.
hrzn_EquitySalesAgreementRemainingAmountAvailableForIssuance
Equity Sales Agreement, Remaining Amount Available for Issuance
The remaining amount available for issuance under equity sales agreement.
hrzn_StockRepurchasedDuringPeriodPerShare
Stock Repurchased During Period, Per Share (in dollars per share)
Per share value of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.
Distributions [Policy Text Block]
The disclosure for the accounting policy related to distributions.
hrzn_BaseManagementAndIncentiveFeesAmountWaivedPerQuarter
Base Management and Incentive Fees, Amount Waived per Quarter
The amount of base management and incentive fees waived per quarter.
Net accretion from repurchase of common stock (in dollars per share)
hrzn_BaseManagementAndIncentiveFeesWaived
Base Management and Incentive Fees Waived
The amount of base management and incentive fees that were waived.
hrzn_EquitySalesAgreementMaximumValue
Equity Sales Agreement, Maximum Value
The maximum value issuable under equity sales agreement.
Merger Agreement Fee Waiver [Member]
Represents information pertaining to the merger agreement with a fee waiver.
Changes in assets and liabilities:
December 31, 2028 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
March 31, 2029 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
Preferred stock, shares issued (in shares)
Stock Repurchase Program [Policy Text Block]
The accounting policy for stock repurchase program.
Preferred stock, shares oustanding (in shares)
Preferred stock, shares authorized (in shares)
CR Financial Holdings [Member]
Represents CR financial holdings.
Portion at Fair Value Measurement [Member]
us-gaap_RestrictedCashEquivalents
Restricted investments in money market funds
hrzn_AmountCommittedToInvest
Amount Committed to Invest
Represents the amount committed to invest by the entity.
Reported Value Measurement [Member]
CRFH Joint Venture [Member]
Represents the CRFH joint venture.
Fair Value, by Balance Sheet Grouping [Table]
Preferred stock, par value (in dollars per share)
Investment, Identifier [Axis]
Other Healthcare Sector [Member]
Related to other healthcare sector.
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect
Net decrease in cash, cash equivalents and restricted cash
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents
Total cash, cash equivalents and restricted cash
Estimate of Fair Value Measurement [Member]
us-gaap_CommonStockDividendsPerShareCashPaid
Common Stock, Dividends, Per Share, Cash Paid (in dollars per share)
hrzn_ProceedsFromDebtSecuritiesEndoftermAmount
Proceeds from Debt Securities, End-of-term, Amount
Amount of cash inflow from debt securities.
Performance based incentive fee (Note 3)
Amount of performance based incentive fee.
hrzn_InvestmentCompanyInvestmentIncomeNet
Total investment income
Total investment income
Amount of investment income, net of investment expense for investment company.
New Accounting Pronouncements, Policy [Policy Text Block]
September 30, 2027 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations
Beginning of period
End of period
Cash, cash equivalents and restricted cash:
us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1
Debt Instrument, Convertible, Threshold Consecutive Trading Days
Net realized gain (loss) on investments
hrzn_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetRealizedGainLossIncludedInEarnings
Amount of realized gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).
Unrealized (depreciation) appreciation included in earnings
Amount of unrealized appreciation (depreciation) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).
Hyperfine Inc [Member]
Represents Hyperfine Inc.
Statement [Table]
Ossio Inc [Member]
Represents Ossio Inc.
hrzn_InvestmentsNonaccrualInterestIncome
Investments, Nonaccrual, Interest Income
Amount of interest income on investment, on nonaccrual status.
Avive Solutions Inc [Member]
Represents Avive Solutions Inc.
Treasury Rate [Member]
Represents information pertaining to the treasury rate.
us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Line of Credit Facility, Current Borrowing Capacity
Interest and Fee Income [Member]
Represents interest and fee income.
Base management fee payable (Note 3)
Management Fee Payable
us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Debt Instrument, Basis Spread on Variable Rate
Investments, fair value
hrzn_LiabilitiesAndNetAssets
Total liabilities and net assets
Amount of liabilities and net assets.
us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Line of Credit Facility, Maximum Borrowing Capacity
us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
Line of Credit Facility, Interest Rate at Period End
Equity Securities [Member]
Transfer out of warrant and equity investments
Amount of transfer of financial instrument classified as an asset between investments.
srt_StockRepurchaseProgramAuthorizedAmount1
Share Repurchase Program, Authorized, Amount
us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Line of Credit Facility, Remaining Borrowing Capacity
O 2025 M2 2 Dividends [Member]
Information regarding distributions.
O 2025 M2 1 Dividends [Member]
Information regarding distributions.
March 31, 2028 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
The 2031 Convertible Notes [Member]
Related to the Convertible Notes due 2031.
Ownership [Axis]
us-gaap_LineOfCredit
Long-Term Line of Credit
Ownership [Domain]
Consolidated Entities [Axis]
Consolidated Entities [Domain]
O 2025 M2 3 Dividends [Member]
Information regarding distributions.
O 2025 M7 Dividends [Member]
Information regarding distributions.
us-gaap_ExciseAndSalesTaxes
Excise and Sales Taxes
Commitments to Extend Credit [Member]
Assets
Measurement Frequency [Axis]
Statement [Line Items]
us-gaap_LongTermDebtWeightedAverageInterestRateOverTime
Long-Term Debt, Weighted Average Interest Rate, over Time
Fair Value Hierarchy and NAV [Axis]
Common stock, shares issued (in shares)
Shares outstanding at end of period (in shares)
Common stock, shares outstanding (in shares)
Common stock, shares authorized (in shares)
us-gaap_ProceedsFromConvertibleDebt
Proceeds from Convertible Debt
us-gaap_DividendsPayableCurrentAndNoncurrent
Distributions payable
Common stock, par value $0.001 per share, 100,000,000 shares authorized, 68,511,552 and 45,781,280 shares issued and 66,978,865 and 45,613,815 shares outstanding as of June 30, 2026 and December 31, 2025, respectively
us-gaap_FairValueOfAssetsAcquired
Fair Value of Assets Acquired
hrzn_DebtInstrumentInterestRateIncreaseFromDefault
Debt Instrument, Interest Rate, Increase From Default
Pertains to the term of the agreement.
hrzn_DebtInstrumentInterestRateIncreaseFromFailureToMaintainInvestmentRating
Debt Instrument, Interest Rate, Increase From Failure to Maintain Investment Rating
Pertains to the term of the agreement.
hrzn_DebtInstrumentConvertibleMaximumBeneficialOwnershipPercentage
Debt Instrument, Convertible, Maximum Beneficial Ownership Percentage
Information pertaining to the agreement.
Momentum US Bidco LLC [Member]
Pertains to Momentum US Bidco LLC.
Proceeds from issuance of common stock, net of offering costs
Proceeds from Issuance of Common Stock
Other accrued expenses
MRCC [Member]
Represents information pertaining to MRCC.
us-gaap_PolicyTextBlockAbstract
Accounting Policies
us-gaap_DisclosureTextBlockAbstract
Notes to Financial Statements
Stellar Cyber, Inc. [Member]
Represents information pertaining to Stellar Cyber, Inc.
us-gaap_TableTextBlock
Notes Tables
hrzn_AssetAcquisitionPercentageOwnedAfterMergerByLegacyStockholders
Asset Acquisition, Percentage Owned After Merger by Legacy Stockholders
Represents the percentage owned after a merger or asset acquisition by the legacy stockholders.
Advances on Credit Facilities
hrzn_AssetAcquisitionPercentageOwnedAfterMergerByFormerStockholdersOfAcquiree
Asset Acquisition, Percentage Owned After Merger by Former Stockholders of Acquiree
Represents the percentage owned after a merger or asset acquisition by the former stockholders of the acquiree.
hrzn_AssetAcquisitionNumberOfSharesIssuedForEachShareOfAcquireesCommonStock
Asset Acquistion, Number of Shares Issued For Each Share of Acquiree's Common Stock (in shares)
Represents the number of shares issued for each share of the acquiree's common stock in relation to an asset acquisition.
MRCC Merger [Member]
Represents information pertaining to the MRCC merger.
Concentration Risk [Table]
Warrants received in settlement of fee income
Amount of warrants received in settlement of fee income.
Subsequent Events [Text Block]
Concentration Risk Type [Axis]
Concentration Risk Disclosure [Text Block]
Asset-backed Notes 2019 [Member]
Represents 2019 asset-backed notes.
Refinanced debt investment balances
Amount of refinanced debt investment balances in noncash transaction.
Three Investments [Member]
Represents three investments.
hrzn_IncentiveFeeCapAndDeferralMechanismReductionToExpense
Incentive Fee Cap and Deferral Mechanism Reduction to Expense
Amount of inventive fee cap and deferral mechanism reduction to expense.
Investment Holdings, Schedule of Investments [Table Text Block]
Schedule of Related Party Transactions [Table Text Block]
RoHo Capital Opportunity LLC [Member]
Represents information pertaining to RoHo Capital Opportunity LLC.
Fair Value, Assets Measured on Recurring Basis [Table Text Block]
Joint Venture Investment Funds [Member]
Represents information pertaining to joint venture investment funds.
hrzn_InvestmentCompanyIncentiveFeePayableExpired
Investment Company, Incentive Fee Payable Expired
Amount of incentive fee payable expired for an investment company.
Concentration Risk Type [Domain]
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Balance
Balance
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table]
Havenly, Inc. [Member]
Represents Havenly, Inc.
us-gaap_PaymentsOfFinancingCosts
Debt issuance costs
Total borrowings outstanding, net
Borrowings (Note 7)
Offsetting Assets [Table]
Net investment income with incentive fees
hrzn_InvestmentCompanyInvestmentIncomeLossRatioAfterIncentiveAllocationExcludingVoluntaryFeeWaiver
Percentage, before deduction of voluntary fee waiver and after incentive allocation, of investment income (loss) to average net assets.
HiveMQ Inc. [Member]
Represents information pertaining to HiveMQ Inc.
Phigenics Holdings, Inc. [Member]
Represents information pertaining to Phigenics Holdings, Inc.
Statement of Stockholders' Equity [Abstract]
Glass Routes, LLC [Member]
Represents information pertaining to Glass Routes, LLC.
Statement of Cash Flows [Abstract]
O 2026 M5 3 Dividends [Member]
Information regarding distributions.
O 2026 M5 4 Dividends [Member]
Information regarding distributions.
O 2026 M5 1 Dividends [Member]
Information regarding distributions.
O 2026 M5 2 Dividends [Member]
Information regarding distributions.
Net assets
O 2026 M10 Dividends [Member]
Information regarding distributions.
Equity Components [Axis]
O 2026 M11 Dividends [Member]
Information regarding distributions.
Unfunded Loan Commitment [Member]
O 2026 M9 Dividends [Member]
Information regarding distributions.
us-gaap_PaymentsOfStockIssuanceCosts
Payments of Stock Issuance Costs
Expenses without incentive fees
O 2026 M2 2 Dividends [Member]
Information regarding distributions.
O 2026 M2 3 Dividends [Member]
Information regarding distributions.
O 2026 M5 5 Dividends [Member]
Information regarding distributions.
O 2026 M5 6 Dividends [Member]
Information regarding distributions.
Offsetting Liabilities [Table Text Block]
Equity Component [Domain]
Offsetting Liabilities [Table]
Fair Value, Inputs, Level 2 [Member]
S 2026 M11 Dividends [Member]
Information regarding distributions.
Fair Value, Inputs, Level 3 [Member]
S 2026 M9 Dividends [Member]
Information regarding distributions.
Equity [Text Block]
Fair Value, Inputs, Level 1 [Member]
S 2026 M10 Dividends [Member]
Information regarding distributions.
Additional Paid-in Capital [Member]
us-gaap_InvestmentCompanyRealizedAndUnrealizedGainLossOnInvestmentAndForeignCurrency
Net realized and unrealized loss
Retained Earnings [Member]
Asset Acquisition [Domain]
Asset Acquisition [Table]
StarCompliance Midco, LLC [Member]
Represents information pertaining to StarCompliance Midco, LLC.
Asset Acquisition [Axis]
Financial Instruments Disclosure [Text Block]
us-gaap_AssetAcquisitionConsiderationTransferred
Asset Acquisition, Consideration Transferred
us-gaap_AssetAcquisitionConsiderationTransferredTransactionCost
Asset Acquisition, Consideration Transferred, Transaction Cost
Subsequent Event Type [Domain]
The 6.25% Notes due 2027 [Member]
Represents the 6.25% Notes due 2027.
Subsequent Event [Table]
Subsequent Event Type [Axis]
Sale of Stock [Axis]
Industry Sector [Domain]
Fair Value Disclosures [Text Block]
Supplemental disclosure of cash flow information:
Investments in and Advances to Affiliates, Schedule of Investments [Text Block]
Accrued interest converted to common stock
Net realized loss on investments
Net realized gain (loss)
hrzn_InvestmentIncomeNetOfExciseTax
Net investment income, net of excise tax
Represents the amount of investment income, net of excise tax.
Sparkcharge, Inc. [Member]
Represents information pertaining to Sparkcharge, inc.
Schedule of Investments [Text Block]
Net realized and unrealized loss
Ceiling
The ceiling rate of the investment owned.
Energy Efficiency [Member]
Represents Energy Efficiency.
Long Grove Pharmaceuticals, LLC [Member]
Related to Long Grove Pharmaceuticals, LLC
MML US, Inc [Member]
Related to MML US, Inc.
us-gaap_PaymentsToAcquireInvestments
Payments to Acquire Investments
ETP
The end of term payment rate (ETP) on investment owned.
hrzn_AssetAcquisitionNumberOfSharesIssued
Asset Acquisition, Number of Shares Issued (in shares)
Represents the number of shares transferred in an asset acquisition.
General and administrative
Supply Network Visibility Holdings, LLC [Member]
Related to Supply Network Visibility Holdings, LLC.
Net realized loss on extinguishment of debt
Gain (Loss) on Extinguishment of Debt
Net realized loss on extinguishment of debt
Paid-in capital in excess of par
us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage
Debt Disclosure [Text Block]
Three Year I Curve [Member]
Related to the Three Year I Curve.
Segment Reporting, Policy [Policy Text Block]
Debt Conversion, Name [Domain]
Debt Conversion Description [Axis]
Use of Estimates, Policy [Policy Text Block]
Noncash or Part Noncash Acquisitions by Unique Description [Axis]
us-gaap_DebtInstrumentConvertibleNumberOfEquityInstruments
Debt Instrument, Convertible, Number of Equity Instruments
us-gaap_EarningsPerShareBasicUndistributed
Earnings Per Share, Basic, Undistributed (in dollars per share)
Issuance of common stock, net of offering costs
Issuance of common stock, net of offering costs
us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Subsidiary, Ownership Percentage, Noncontrolling Owner
us-gaap_MinorityInterestOwnershipPercentageByParent
Subsidiary, Ownership Percentage, Parent
Balance outstanding
us-gaap_DebtInstrumentFairValue
Debt Instrument, Fair Value Disclosure
Issuance of common stock under dividend reinvestment plan
Investments in money market funds
Issuance of common stock in extinguishment of debt
Total commitment
Debt Instrument, Face Amount
Issuance of common stock pursuant to Merger Agreement
Schedule of Debt [Table Text Block]
Asset Acquisition [Text Block]
Fair Value, Recurring and Nonrecurring [Table]
Issuance of common stock, net of offering costs (in shares)
Stock Issued During Period, Shares, New Issues (in shares)
Issuance of common stock, net of offering costs (in shares)
Transfers and Servicing of Financial Assets, Servicing of Financial Assets, Policy [Policy Text Block]
Issuance of common stock in extinguishment of debt (in shares)
Industry Sector [Axis]
Debt Instrument, Name [Domain]
Issuance of common stock under dividend reinvestment plan (in shares)
Base management fee (Note 3)
Management Fee Expense
Fair Value Measurement Inputs and Valuation Techniques [Table Text Block]
Issuance of common stock pursuant to Merger Agreement (in shares)
us-gaap_DebtInstrumentMaturityDate
Debt Instrument, Maturity Date
Administrative fee (Note 3)
Administrative Fees Expense
us-gaap_DebtInstrumentInterestRateStatedPercentage
Debt Instrument, Interest Rate, Stated Percentage
Fair Value Measurement Inputs and Valuation Techniques [Table]
us-gaap_IncentiveFeeExpense
Incentive Fee Expense
Class of Stock [Domain]
Schedule of Long-Term Debt Instruments [Table]
Debt Instrument [Axis]
Noncash or Part Noncash Acquisition, Name [Domain]
us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet
Unamortized debt issuance costs attributable to term borrowings
Unused commitment
Cash flows from operating activities:
Debt Securities [Member]
us-gaap_NetCashProvidedByUsedInOperatingActivities
Net cash provided by operating activities
Cash flows from financing activities:
us-gaap_NetCashProvidedByUsedInFinancingActivities
Net cash used in financing activities
Debt [Member]
Stockholders' Equity, Policy [Policy Text Block]
hrzn_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPaymentInkindInterest
PIK interest on investments
Amount of payment in-king interest on financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.
us-gaap_DebtInstrumentRedemptionPricePercentage
Debt Instrument, Redemption Price, Percentage
Average net asset value
hrzn_AverageNetAssets
Amount of average net assets (liabilities).
Common Stock Outstanding [Member]
Represents common stock outstanding.
Software, Healthcare Information and Service [Member]
Represents software for healthcare information and service.
Accounting Policies [Abstract]
Contributions receivable
us-gaap_AccumulatedAmortizationDeferredFinanceCosts
Accumulated Amortization, Debt Issuance Costs
us-gaap_DebtInstrumentConvertibleStockPriceTrigger
Debt Instrument, Convertible, Stock Price Trigger (in dollars per share)
From net investment income (in dollars per share)
hrzn_InvestmentCompanyDistributionToShareholdersPerShareNetInvestmentIncome
Per share or unit amount of distribution from net investment income to shareholders.
Bastille Buyer, Inc. [Member]
Represents information pertaining to Bastille Buyer, Inc.
Volt Bidco, Inc. [Member]
Represents information pertaining to Volt Bidco, Inc.
From net realized gain on investments (in dollars per share)
hrzn_InvestmentCompanyDistributionToShareholdersPerShareNetRealizedGainOnInvestments
Per share or unit amount of distribution from net realized gain on investments to shareholders.
Other (in dollars per share)
Per share or unit amount of distribution from other sources not separately classified to shareholders.
Unrealized depreciation on investments (in dollars per share)
hrzn_InvestmentCompanyInvestmentDepreciationAppreciationPerShare
Per share or unit amount, after investment expense, of (depreciation) appreciation.
us-gaap_StockRepurchasedDuringPeriodValue
Stock Repurchased During Period, Value
Repurchase of common stock
us-gaap_StockRepurchasedDuringPeriodShares
Stock Repurchased During Period, Shares (in shares)
Repurchase of common stock (in shares)
hrzn_PolicyTable
Measurement Input Type [Axis]
Income Statement [Abstract]
us-gaap_UnrecognizedTaxBenefits
Unrecognized Tax Benefits, Ending Balance
Average debt per share (in dollars per share)
hrzn_InvestmentCompanyAverageDebtPerShare
The average debt per share in investment company.
us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Numerator for diluted earnings per share
Portfolio turnover ratio
hrzn_InvestmentCompanyPortfolioTurnoverRatio
The portfolio turnover ratio for investment company.
us-gaap_MembersEquity
Total members’ capital
Measurement Input, Discount Rate [Member]
Measurement Input, Discount for Lack of Marketability [Member]
Net decrease in net assets resulting from operations
Net decrease in net assets resulting from operations
Net decrease in net assets resulting from operations
Measurement Input, Price Volatility [Member]
Numerator for decrease in net assets per share
Numerator for basic earnings per share
Adjustment for interest expense and debt issuance costs on Convertible Notes
Record date
Amortization of debt issuance costs
Amortization of Debt Issuance Costs
Members’ capital
Valuation Technique, Discounted Cash Flow [Member]
Expenses
us-gaap_NetInvestmentIncome
Net investment income before excise tax
Measurement Input, Share Price [Member]
Measurement Input Type [Domain]
Net assets at the end of the period
hrzn_NetAssets
Total net assets
Amount of net assets (liabilities).
Interest (reversal) income
us-gaap_OtherCommitment
Other Commitment
Debt converted to common stock
Debt Conversion, Original Debt, Amount
us-gaap_DebtInstrumentMeasurementInput
Debt Instrument, Measurement Input
us-gaap_DebtConversionConvertedInstrumentSharesIssued1
Debt Conversion, Converted Instrument, Shares Issued (in shares)
us-gaap_CostsAndExpenses
Total expenses
Total expenses
hrzn_AdministrativeFeesPayable
Administrative Fees Payable
Amount of payable for administrative fees.
Four Investments [Member]
Represents four investments.
December 31, 2026 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
HIMV LLC [Member]
Accounting Standards Update and Change in Accounting Principle [Table]
Net assets acquired
Income Tax, Policy [Policy Text Block]
Non-cash income
September 30, 2026 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
Horizon Technology Finance Corporation [Member]
Information by consolidated entity or group of entities.
Co-lender [Member]
Information pertaining to the co-lender.
Assets of Powerscourt Investments XXV, LP [Member]
Represents assets of Powerscourt Investments XXV, LP.
Debt Investments [Member]
Related to debt investments.
hrzn_StockRepurchaseProgramMaximumPercentageOfNetAssetValue
Stock Repurchase Program, Maximum Percentage of Net Asset Value
Maximum percentage of net asset value for repurchase of stock under the program.
hrzn_StockRepurchaseProgramPercentageOfOutstandingStockMaximum
Stock Repurchase Program, Percentage of Outstanding Stock Maximum
Maximum number of shares that may be repurchased in accordance with the plan as a proportion of outstanding capital stock.
us-gaap_DeferredFinanceCostsNet
Debt Issuance Costs, Net
Investment Concentration Risk [Member]
Related to investment concentration risk.
Related Party Transaction [Table]
Ceribell, Inc. [Member]
Related to Ceribell, Inc.
Related Party Transactions Disclosure [Text Block]
Britecore Holdings, Inc. [Member]
Related to Britecore Holdings, Inc.
Collaborative Arrangement and Arrangement Other than Collaborative [Axis]
Measurement Basis [Axis]
Dividends Declared [Table Text Block]
Prepayment fee income
Amount of income for prepayment fee on investment.
Other Investment [Member]
Represents other investments.
Key Facility [Member]
Related to Key Facility.
NYL Facility [Member]
Related to NYL Facility.
Fair Value Hierarchy and NAV [Domain]
The 2027 Notes [Member]
Related to the 2027 notes.
Measurement Frequency [Domain]
Sonex Health, Inc. [Member]
Related to Sonex Health, Inc.
us-gaap_OpenTaxYear
Open Tax Year
us-gaap_RepaymentsOfLinesOfCredit
Repayment of Credit Facilities
Statement of Financial Position [Abstract]
The 2026 Notes [Member]
Related to the 2026 notes.
Payment date
Mirantis, Inc [Member]
Represents Mirantis, Inc.
hrzn_LineOfCreditFacilityMaximumBorrowingCapacityAccordianFeature
Line of Credit Facility, Maximum Borrowing Capacity, Accordian Feature
Maximum borrowing capacity under the credit facility after the accordion feature increase.
hrzn_LineOfCreditFacilityAdvanceRateOfEligibleDebtInvestments
Line of Credit Facility, Advance Rate of Eligible Debt Investments
The advance rate of eligible debt investments under line of credit facility.
us-gaap_RepaymentsOfNotesPayable
Repayment of note
hrzn_AssetCoverageToBorrowingsRatioPercent
Asset Coverage to Borrowings, Ratio, Percent
The asset coverage to borrowings ratio percentage.
hrzn_InvestmentIncomeAttributableToNoncashPaidinkindInterestPercent
Investment, Income Attributable to Non-cash Paid-in-Kind Interest, Percent
The percent of investment income attributable to non-cash PIK interest.
Principal payments received on investments
Other assets
hrzn_DebtInstrumentVariableRate
Debt Instrument, Variable Rate
The variable rate of debt instrument.
Professional fees
Fair Value, Recurring [Member]
Conversion of 2031 Notes Into Common Stock [Member]
Represents the conversion of the 2031 notes into common stock.
O 2025 M4 1 Dividends [Member]
Information regarding distributions.
O 2025 M4 2 Dividends [Member]
Information regarding distributions.
us-gaap_PaymentsForRepurchaseOfCommonStock
Repurchase of common stock
us-gaap_IncreaseDecreaseInOtherOperatingAssets
Decrease (increase) in other assets
Warrant [Member]
us-gaap_ConvertibleDebt
Convertible Debt
Net asset value per common share (in dollars per share)
Net asset value at beginning of period (in dollars per share)
Net asset value at end of period (in dollars per share)
Document Type
Document Information [Line Items]
Document Quarterly Report
us-gaap_ConcentrationRiskPercentage1
Concentration Risk, Percentage
O 2025 M4 3 Dividends [Member]
Information regarding distributions.
Document Information [Table]
Entity Interactive Data Current
Document Transition Report
Weighted average shares outstanding - diluted (in shares)
The 2023 Equity Distribution Agreement [Member]
Represents the 2023 Equity Distribution Agreement.
us-gaap_GainLossOnSaleOfInvestments
Net realized loss on investments
Adjustment for dilutive effect of Convertible Notes (in shares)
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities (in shares)
us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Denominator for basic weighted average shares (in shares)
Net unrealized appreciation (depreciation) on investments
Net unrealized appreciation (depreciation) on non-affiliate investments
Unrealized Gain (Loss) on Investments
Net unrealized depreciation on investments
us-gaap_EarningsPerShareBasic
Loss per common share - basic (in dollars per share)
Stock consideration
Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table]
hrzn_RealizedInvestmentGainsLossesNetOfDebtExtinguishment
Net realized loss
Amount of realized gain (loss) on investment, net of debt extinguishment.
Collaborative Arrangement and Arrangement Other than Collaborative [Domain]
MasteryPrep, LLC [Member]
Represents information pertaining to MasteryPrep, LLC
June 30, 2028 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
Document Fiscal Period Focus
Document Fiscal Year Focus
Investment, Name [Domain]
Amendment Flag
Common Stock [Member]
Net realized loss on extinguishment of debt
hrzn_RealizedGainlossExtinguishmentOfDebt
Net realized loss on extinguishment of debt
The amount of realized gain or loss from the extinguishment of debt.
Maturity Date
Document Period End Date
Restricted investments in money market funds
Restricted Investments
Investment [Table Text Block]
Investment income
Legal Entity [Axis]
Business Combination [Domain]
Entity File Number
Entity Tax Identification Number
Supplemental non-cash operating and financing activities:
Business Combination [Axis]
Entity [Domain]
Entity Central Index Key
Entity Registrant Name
Entity Current Reporting Status
Entity Incorporation, State or Country Code
Current Fiscal Year End Date
Fair Value Measurement, Policy [Policy Text Block]
Entity Filer Category
Entity Shell Company
Entity Emerging Growth Company
Entity Small Business
Dividends, shares (in shares)
Investments [Domain]
Valuation Approach and Technique [Axis]
Cash
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Interest expense
Valuation Approach and Technique [Domain]
The 2026 Notes Underwriter Option [Member]
Related to the 2026 notes underwriter option.
The 2027 Notes Underwriter Option [Member]
Related to the 2027 Notes underwriter option.
hrzn_LineOfCreditFacilityChangeInMaximumBorrowingCapacity
Line of Credit Facility, Change in Maximum Borrowing Capacity
The change in maximum borrowing capacity in line of credit facility.
Other
Amount of other increase (decrease) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.
Entity Address, State or Province
Incentive Fee Cap and Deferral Mechanism, Contingent Future Liability
Amount of contingent future liability from Incentive Fee Cap and Deferral Mechanism.
Warrants and equity received and classified as Level 3
Warrants received and classified as Level 3
Amount of received warrants and equity received of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.
Entity Address, City or Town
Distributable loss
Entity Address, Address Line One
hrzn_LineOfCreditFacilityMaximumBorrowingCapacityAccordionFeature
Line of Credit Facility, Maximum Borrowing Capacity, Accordion Feature
The accordion feature for the maximum borrowing capacity under line of credit facility.
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]
hrzn_LineOfCreditFacilityAdvanceRate
Line of Credit Facility, Advance Rate
The advance rate under line of credit facility.
City Area Code
Estimated Time to Exit [Member]
Related to Estimated Time to Exit.
Last Equity Financing [Member]
Related to Last Equity Financing.
Investments, measurement input
Value of input used to measure investment assets.
Local Phone Number
Entity Address, Postal Zip Code
Hypothetical Market Yield [Member]
Related to Hypothetical Market Yield.
Multiple Probability Weighted Cash Flow Model [Member]
Related to Multiple Probability Weighted Cash Flow Model.
Probability Weighting [Member]
Related to Probability Weighting.
Black-scholes Valuation Model [Member]
Related to Black-Scholes Valuation Model.
Title of 12(b) Security
Security Exchange Name
Trading Symbol
us-gaap_DebtInstrumentConvertibleConversionPrice1
Debt Instrument, Convertible, Conversion Price (in dollars per share)
Class of Stock [Axis]
Prime Rate [Member]
Variable Rate [Axis]
Variable Rate [Domain]
Entity Common Stock, Shares Outstanding
Earnings Per Share [Text Block]
Weighted average shares outstanding - basic (in shares)
Other Debt Obligations [Member]
Merger expenses
Unfunded commitments, principal balance
us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
Fair value of unfunded commitment liability
us-gaap_FairValueDisclosureOffbalanceSheetRisksAmountLiability
Fair Value Disclosure, off-Balance-Sheet Risks, Amount, Liability
The 2028 Notes [Member]
Represents information pertaining to the 2028 notes.
Margin
Percentage added to reference rate used to compute variable rate on investment.
Scenario [Axis]
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Principal payments received on investments
Scenario [Domain]
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Proceeds from sale of investments
Forecast [Member]
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Purchase of investments
us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments
Proceeds from Sale, Maturity and Collection of Investments
Common stock, par value (in dollars per share)
Investment, Name [Axis]
Other liabilities
Measurement Input, Hypothetical Market Yields [Member]
Related to hypothetical market yields used as measurement input.
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3
Transfer out of Level 3
hrzn_DebtInstrumentSharePrice
Debt Instrument, Share Price (in dollars per share)
The share price of a debt investment instrument.
us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3
Sale of Stock [Domain]
Transfers in/(out) at fair value
Transfer amount changes to the investment in and advance to the affiliate.
us-gaap_Assets
Total assets
Samba TV, Inc. [Member]
Represents information pertaining to Samba TV, Inc.
us-gaap_CashAcquiredFromAcquisition
Cash Acquired from Acquisition
O 2025 M10 1 Dividends [Member]
Information regarding distributions.
O 2025 M10 3 Dividends [Member]
Information regarding distributions.
O 2025 M10 2 Dividends [Member]
Information regarding distributions.
Investments at fair value
Investments, fair value
Investments, fair value
O 2026 M2 Dividends [Member]
Information regarding distributions.
Discount accretion
Discount accretion to the investment in and advance to the affiliate.
Investments in and Advances to Affiliates [Table Text Block]
Investments in and Advances to Affiliates [Table]
Investment Holdings [Text Block]
O 2025 M7 3 Dividends [Member]
Information regarding distributions.
O 2025 M7 2 Dividends [Member]
Information regarding distributions.
Loss per common share - diluted (in dollars per share)
Biotechnology Sector [Member]
Related to biotechnology sector.
Medical Device Sector [Member]
Related to medical device sector.
Number of Shares (in shares)
Communications Sector [Member]
Related to communications sector.
Consumer-related Sector [Member]
Related to consumer-related sector.
us-gaap_PaymentsForPurchaseOfSecuritiesOperatingActivities
Purchase of investments
Pelthos Therapeutics, Inc. [Member]
Represents information pertaining to Pelthos Therapeutics, Inc.
Investment Company, Financial Highlights [Text Block]
Debt, Policy [Policy Text Block]
Investment Holdings [Table]
Investment Company, Financial Highlights [Table Text Block]
Software Sector [Member]
Related to software sector.
Other Sustainability Sector [Member]
Related to other sustainability sector.
Diagnostics Sector [Member]
Related to diagnostics sector.
Proceeds from sale of investments
Data Storage Sector [Member]
Related to data storage sector.
Internet and Media Sector [Member]
Related to internet and media sector.
Networking Sector [Member]
Related to networking sector.
hrzn_IncentiveFeeToPreincentiveNetInvestmentIncome
Incentive Fee to Pre-incentive Net Investment Income
The incentive fee to pre-incentive net investment income.
us-gaap_InvestmentCompanyDistributionToShareholdersPerShare
Distributions (in dollars per share)
hrzn_PreincentiveFeeNetInvestmentIncomeHurdleRate
Pre-Incentive Fee Net Investment Income, Hurdle Rate
The hurdle rate for pre-inventive fee net investment income.
Return of capital (in dollars per share)
us-gaap_InvestmentCompanyTaxReturnOfCapitalDistributionPerShare
Investment Type [Axis]
hrzn_PreincentiveFeeNetInvestmentIncomeHurdleRateAnnualized
Pre-Incentive Fee Net Investment Income, Hurdle Rate, Annualized
The annualized pre-incentive fee net investment income hurdle rate.
September 30, 2028 Expiration [Member]
Represents information pertaining to the September 30, 2028 expiration.
hrzn_PreincentiveFeeNetInvestmentIncomeCatchupPercent
Pre-Incentive Fee Net Investment Income, Catch-up, Percent
The percent catch-up for pre-incentive fee net investment income.
Net investment income (in dollars per share)
us-gaap_InvestmentCompanyInvestmentIncomeLossPerShare
Investment Company, Investment Income (Loss), Per Share, Basic (in dollars per share)
hrzn_BaseManagementFeeAnnualPercent
Base Management Fee, Annual, Percent
The annual percentage base management fee.
Realized loss (in dollars per share)
Principal Amount
Investment Company, Financial Highlights [Table]
Consolidation, Policy [Policy Text Block]
hrzn_BaseManagementFeeAnnualPercentGrossAssetsExceeding250Million
Base Management Fee, Annual, Percent, Gross Assets Exceeding $250 Million
The annual percentage base management fee for gross assets exceeding $250 million.
Investments at cost
Investment Management Agreement [Member]
Related to Investment Management Agreement.
Total return based on a market value
us-gaap_InvestmentCompanyTotalReturn
The 2030 Convertible Notes [Member]
Represents information pertaining to the 2030 Convertible Notes.
Interest receivable
Interest income
Interest income
hrzn_PreincentiveFeeNetInvestmentIncomeMaximumRateToTriggerCatchup
Pre-Incentive Fee Net Investment Income, Maximum Rate to Trigger Catch-up
The maximum rate to trigger catch-up for pre-incentive fee net investment income.
Cash paid for interest
hrzn_PreincentiveFeeNetInvestmentIncomeMaximumRateToTriggerCatchupAnnualized
Pre-Incentive Fee Net Investment Income, Maximum Rate to Trigger Catch-up, Annualized
The annualized maximum rate to trigger catch-up for pre-incentive fee net investment income.
Net expenses
us-gaap_InvestmentCompanyExpenseRatioIncludingIncentiveFee
Administration Agreement [Member]
Related to administration agreement.
Incentive fees
us-gaap_InvestmentCompanyIncentiveFeeToAverageNetAssets
Net decrease in net assets resulting from operations per common share - diluted (1) (in dollars per share)
Per share or unit amount of increase (decrease) in net asset value, diluted.
December 31, 2027 Expiration [Member]
Represents information pertaining to the expiration of the total contingent future liability.
us-gaap_InvestmentCompanyDividendDistribution
Distributions declared
Onkos Surgical, Inc. [Member]
Related to Onkos Surgical, Inc.
Crafty Holdings, Inc.[Member]
Related to Crafty Holdings, Inc.
Investment, Affiliated Issuer, Controlled [Member]
us-gaap_StockholdersEquity
Balance
Balance
Investment, Affiliated Issuer, Noncontrolled [Member]
Investment, Unaffiliated Issuer [Member]
Investment, Issuer Affiliation [Axis]
hrzn_DebtInstrumentConvertibleAcceleratedUnamortizedDebtIssuanceCosts
Debt Instrument, Convertible, Accelerated Unamortized Debt Issuance Costs
The accelerated unamortized debt issuance costs for convertible debt instruments.
Investment, Issuer Affiliation [Domain]
hrzn_DebtInstrumentConvertibleWeightedAverageConversionPrice
Debt Instrument, Convertible, Weighted Average Conversion Price (in dollars per share)
The weighted average conversion price for convertible debt instruments.
Conversion of 2030 Notes Into Common Stock [Member]
Represents information pertaining to the conversion of 2030 notes into common stock.
us-gaap_PaymentsOfDividends
Distributions paid
Investment, Issuer Name [Axis]
Investment, Issuer Name [Domain]
Concentration Risk Benchmark [Axis]
us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossReductions
Reductions
Nature of Operation, Product Information, Concentration of Risk [Table]
Concentration Risk Benchmark [Domain]
Purchases
ecd_Rule10b51ArrTrmntdFlag
Rule 10b5-1 Arrangement Terminated [Flag]
ecd_Rule10b51ArrAdoptedFlag
Rule 10b5-1 Arrangement Adopted [Flag]
Cash Rate
Floor
Commitments and contingencies (Notes 3 and 8)