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.

Name:	us-gaap_DebtInstrumentCarryingAmount
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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69C
-URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI https://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69B
-URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399

+ Details

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

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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

- Definition

Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI https://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69C
-URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
-Paragraph 69B
-URI https://asc.fasb.org/extlink&oid=123466577&loc=SL123495735-112612

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1D
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Period between issuance and maturity of long-term debt, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

+ Details

Name:	us-gaap_LongTermDebtTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

Prospect Capital InterNotes® - Schedule of Notes Outstanding (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Principal Outstanding	$ 2,670,175	$ 2,769,156
Net borrowings	2,640,020	2,737,276
Prospect Capital InterNotes
Debt Instrument [Line Items]
Unamortized debt issuance	(6,969)	(7,122)
Prospect Capital InterNotes \| Unsecured Debt
Debt Instrument [Line Items]
Principal Outstanding	349,044	347,564
Unamortized debt issuance	(6,969)	(7,122)
Net borrowings	$ 342,075	$ 340,442
Weighted Average Interest Rate	4.50%		3.35%
Prospect Capital InterNotes \| Unsecured Debt \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	4.50%		2.25%
Prospect Capital InterNotes \| Unsecured Debt \| Maximum
Debt Instrument [Line Items]
Interest Rate Range			4.00%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2024 – March 15, 2025
Debt Instrument [Line Items]
Tenor at Origination (in years)	3 years	3 years
Principal Outstanding	$ 2,161	$ 2,161
Weighted Average Interest Rate	2.19%	2.19%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2024 – March 15, 2025 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	1.50%	1.50%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2024 – March 15, 2025 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	2.50%	2.50%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2026 – September 15, 2027
Debt Instrument [Line Items]
Tenor at Origination (in years)	5 years
Principal Outstanding	$ 97,758
Weighted Average Interest Rate	3.30%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2026 – September 15, 2027 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	2.25%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2026 – September 15, 2027 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	4.50%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2026 – June 15, 2027
Debt Instrument [Line Items]
Tenor at Origination (in years)		5 years
Principal Outstanding		$ 95,134
Weighted Average Interest Rate		3.27%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2026 – June 15, 2027 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range		2.25%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2026 – June 15, 2027 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range		4.50%
Prospect Capital InterNotes \| Unsecured Debt \| June 15, 2027 – July 15, 2027
Debt Instrument [Line Items]
Tenor at Origination (in years)	6 years	6 years
Principal Outstanding	$ 15,007	$ 15,057
Interest Rate Range	3.00%	3.00%
Weighted Average Interest Rate	3.00%	3.00%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2028 – February 15, 2029
Debt Instrument [Line Items]
Tenor at Origination (in years)	7 years	7 years
Principal Outstanding	$ 29,252	$ 29,252
Weighted Average Interest Rate	3.17%	3.17%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2028 – February 15, 2029 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	2.75%	2.75%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2028 – February 15, 2029 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	4.25%	4.25%
Prospect Capital InterNotes \| Unsecured Debt \| June 15, 2029 – July 15, 2029
Debt Instrument [Line Items]
Tenor at Origination (in years)	8 years	8 years
Principal Outstanding	$ 3,511	$ 3,511
Weighted Average Interest Rate	3.45%	3.45%
Prospect Capital InterNotes \| Unsecured Debt \| June 15, 2029 – July 15, 2029 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	3.40%	3.40%
Prospect Capital InterNotes \| Unsecured Debt \| June 15, 2029 – July 15, 2029 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	3.50%	3.50%
Prospect Capital InterNotes \| Unsecured Debt \| August 15, 2029 – May 15, 2032
Debt Instrument [Line Items]
Tenor at Origination (in years)	10 years	10 years
Principal Outstanding	$ 77,291	$ 77,434
Weighted Average Interest Rate	3.85%	3.85%
Prospect Capital InterNotes \| Unsecured Debt \| August 15, 2029 – May 15, 2032 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	3.15%	3.15%
Prospect Capital InterNotes \| Unsecured Debt \| August 15, 2029 – May 15, 2032 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	4.50%	4.50%
Prospect Capital InterNotes \| Unsecured Debt \| June 15, 2033 – July 15, 2033
Debt Instrument [Line Items]
Tenor at Origination (in years)	12 years	12 years
Principal Outstanding	$ 14,946	$ 15,066
Weighted Average Interest Rate	3.95%	3.95%
Prospect Capital InterNotes \| Unsecured Debt \| June 15, 2033 – July 15, 2033 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	3.70%	3.70%
Prospect Capital InterNotes \| Unsecured Debt \| June 15, 2033 – July 15, 2033 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	4.00%	4.00%
Prospect Capital InterNotes \| Unsecured Debt \| July 15, 2036 – February 15, 2037
Debt Instrument [Line Items]
Tenor at Origination (in years)	15 years	15 years
Principal Outstanding	$ 14,836	$ 15,041
Weighted Average Interest Rate	3.84%	3.84%
Prospect Capital InterNotes \| Unsecured Debt \| July 15, 2036 – February 15, 2037 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	3.50%	3.50%
Prospect Capital InterNotes \| Unsecured Debt \| July 15, 2036 – February 15, 2037 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	4.50%	4.50%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2031 – April 15, 2031
Debt Instrument [Line Items]
Tenor at Origination (in years)	18 years	18 years
Principal Outstanding	$ 3,085	$ 3,085
Weighted Average Interest Rate	4.73%	4.73%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2031 – April 15, 2031 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	4.50%	4.50%
Prospect Capital InterNotes \| Unsecured Debt \| January 15, 2031 – April 15, 2031 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	5.00%	5.00%
Prospect Capital InterNotes \| Unsecured Debt \| November 15, 2032
Debt Instrument [Line Items]
Tenor at Origination (in years)	20 years	20 years
Principal Outstanding	$ 1,597	$ 1,597
Interest Rate Range	5.75%	5.75%
Weighted Average Interest Rate	5.75%	5.75%
Prospect Capital InterNotes \| Unsecured Debt \| November 15, 2038 – May 15, 2039
Debt Instrument [Line Items]
Tenor at Origination (in years)	25 years	25 years
Principal Outstanding	$ 8,036	$ 8,036
Weighted Average Interest Rate	6.37%	6.37%
Prospect Capital InterNotes \| Unsecured Debt \| November 15, 2038 – May 15, 2039 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	6.25%	6.25%
Prospect Capital InterNotes \| Unsecured Debt \| November 15, 2038 – May 15, 2039 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	6.50%	6.50%
Prospect Capital InterNotes \| Unsecured Debt \| November 15, 2042 – March 15, 2052
Debt Instrument [Line Items]
Tenor at Origination (in years)	30 years	30 years
Principal Outstanding	$ 81,564	$ 82,190
Weighted Average Interest Rate	5.30%	5.29%
Prospect Capital InterNotes \| Unsecured Debt \| November 15, 2042 – March 15, 2052 \| Minimum
Debt Instrument [Line Items]
Interest Rate Range	4.00%	4.00%
Prospect Capital InterNotes \| Unsecured Debt \| November 15, 2042 – March 15, 2052 \| Maximum
Debt Instrument [Line Items]
Interest Rate Range	6.63%	6.63%