The asset coverage to borrowings ratio percentage.

No definition available.

Name:	hrzn_AssetCoverageToBorrowingsRatioPercent
Namespace Prefix:	hrzn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The variable rate of debt instrument.

+ References

No definition available.

+ Details

Name:	hrzn_DebtInstrumentVariableRate
Namespace Prefix:	hrzn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The advance rate under line of credit facility.

+ References

No definition available.

+ Details

Name:	hrzn_LineOfCreditFacilityAdvanceRate
Namespace Prefix:	hrzn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The advance rate of eligible debt investments under line of credit facility.

+ References

No definition available.

+ Details

Name:	hrzn_LineOfCreditFacilityAdvanceRateOfEligibleDebtInvestments
Namespace Prefix:	hrzn_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The change in maximum borrowing capacity in line of credit facility.

+ References

No definition available.

+ Details

Name:	hrzn_LineOfCreditFacilityChangeInMaximumBorrowingCapacity
Namespace Prefix:	hrzn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility after the accordion feature increase.

+ References

No definition available.

+ Details

Name:	hrzn_LineOfCreditFacilityMaximumBorrowingCapacityAccordianFeature
Namespace Prefix:	hrzn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The accordion feature for the maximum borrowing capacity under line of credit facility.

+ References

No definition available.

+ Details

Name:	hrzn_LineOfCreditFacilityMaximumBorrowingCapacityAccordionFeature
Namespace Prefix:	hrzn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-4

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-5

+ Details

Name:	us-gaap_DebtInstrumentConvertibleConversionPrice1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482900/835-30-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69B

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69C

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482925/835-30-45-2

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482949/835-30-55-8

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16)(a)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of long-term debt outstanding calculated over time.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermDebtWeightedAverageInterestRateOverTime
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
-SubTopic 210
-Name Accounting Standards Codification
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480632/954-210-45-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480602/954-210-50-2

+ Details

Name:	us-gaap_RestrictedInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=hrzn_KeyFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=hrzn_NYLFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=hrzn_USDMidmarketWwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=hrzn_AssetbackedNotes2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=hrzn_AssetbackedNotes2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=hrzn_The2026NotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=hrzn_The2026NotesUnderwriterOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=hrzn_The2027NotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=hrzn_The2027NotesUnderwriterOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 7 - Borrowings (Details Textual) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	12 Months Ended	21840 Months Ended
	Feb. 25, 2022	Apr. 21, 2020	Mar. 31, 2023	Dec. 31, 2021	Feb. 25, 2022	Dec. 31, 2022	Nov. 09, 2022	Jun. 15, 2022	Jun. 22, 2021	Mar. 30, 2021	Aug. 13, 2019
Asset Coverage to Borrowings, Ratio, Percent			172.00%
Restricted Investments			$ 2,987			$ 2,788
Long-Term Debt, Gross			444,541			439,323
Debt Instrument, Face Amount			$ 577,791			582,573
Key Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity, Accordian Feature									$ 150,000
Line of Credit Facility, Maximum Borrowing Capacity									$ 125,000
Line of Credit Facility, Advance Rate of Eligible Debt Investments									60.00%
Long-Term Debt, Weighted Average Interest Rate, over Time			7.94%	4.25%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.50%
Line of Credit Facility, Current Borrowing Capacity			$ 110,000			120,000
Line of Credit Facility, Remaining Borrowing Capacity			47,700			40,200
Long-Term Debt, Gross			15,000			5,000
Debt Instrument, Face Amount			$ 125,000			$ 125,000
Key Facility [Member] \| Prime Rate [Member]
Debt Instrument, Basis Spread on Variable Rate			0.25%
Debt Instrument, Variable Rate			8.00%			7.50%
NYL Facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200,000	$ 100,000			$ 200,000
Line of Credit Facility, Current Borrowing Capacity			$ 23,200			$ 23,200
Line of Credit Facility, Remaining Borrowing Capacity			21,100			23,200
Line of Credit Facility, Maximum Borrowing Capacity, Accordion Feature		$ 200,000
Line of Credit Facility, Advance Rate		67.00%
Line of Credit Facility, Change in Maximum Borrowing Capacity	$ 100,000
Long-Term Line of Credit			$ 176,800			$ 176,800
Line of Credit Facility, Interest Rate at Period End			5.57%			5.57%
Restricted Investments			$ 1,300			$ 1,000
Long-Term Debt, Gross			176,750			176,750
Debt Instrument, Face Amount			200,000			200,000
NYL Facility [Member] \| USD Mid-market Wwap Rate [Member]
Debt Instrument, Basis Spread on Variable Rate					3.00%
Asset-backed Notes 2019 [Member]
Restricted Investments			500			600
Debt Instrument, Interest Rate, Stated Percentage											4.21%
Long-Term Debt, Gross			37,791			42,573
Debt Instrument, Face Amount			37,791			42,573					$ 160,000
Asset-backed Notes 2022 [Member]
Restricted Investments			1,100			1,000
Debt Instrument, Interest Rate, Stated Percentage							7.56%
Long-Term Debt, Gross			100,000			100,000
Debt Instrument, Face Amount			100,000			100,000	$ 157,800
The 2026 Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage										4.875%
Long-Term Debt, Gross			57,500			57,500
Debt Instrument, Face Amount			57,500			57,500				$ 57,500
The 2026 Notes Underwriter Option [Member]
Debt Instrument, Face Amount										$ 7,500
Debt Instrument, Convertible, Conversion Price (in dollars per share)										$ 25
The 2027 Notes [Member]
Debt Instrument, Interest Rate, Stated Percentage								6.25%
Long-Term Debt, Gross			57,500			57,500
Debt Instrument, Face Amount			$ 57,500			$ 57,500		$ 50,000
The 2027 Notes Underwriter Option [Member]
Debt Instrument, Face Amount								$ 7,500
Debt Instrument, Convertible, Conversion Price (in dollars per share)								$ 25
Minimum [Member]
Asset Coverage to Borrowings, Ratio, Percent			150.00%
Minimum [Member] \| Key Facility [Member] \| Prime Rate [Member]
Debt Instrument, Basis Spread on Variable Rate			4.25%
Minimum [Member] \| NYL Facility [Member] \| USD Mid-market Wwap Rate [Member]
Debt Instrument, Basis Spread on Variable Rate		3.55%
Maximum [Member] \| NYL Facility [Member] \| USD Mid-market Wwap Rate [Member]
Debt Instrument, Basis Spread on Variable Rate		5.15%