Prospect Capital InterNotes® - Schedule of Notes Outstanding (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023
Debt Instrument [Line Items]
Principal Outstanding	$ 2,505,497	$ 2,610,216
Net Carrying Value	2,483,620	2,584,848
Prospect Capital InterNotes®
Debt Instrument [Line Items]
Unamortized debt issuance	(7,403)	(6,688)
Prospect Capital InterNotes® | Unsecured Debt
Debt Instrument [Line Items]
Principal Outstanding	442,953	358,105
Unamortized debt issuance	(7,403)	(6,688)
Net Carrying Value	$ 435,550	$ 351,417
Weighted Average Interest Rate	7.13%		5.41%
Prospect Capital InterNotes® | Unsecured Debt | Minimum
Debt Instrument [Line Items]
Interest Rate Range	5.75%		4.50%
Prospect Capital InterNotes® | Unsecured Debt | Maximum
Debt Instrument [Line Items]
Interest Rate Range	8.00%		5.95%
Prospect Capital InterNotes® | Unsecured Debt | February 15, 2025 – March 15, 2027
Debt Instrument [Line Items]
Tenor at Origination (in years)	3 years
Principal Outstanding	$ 40,378
Weighted Average Interest Rate	6.19%
Prospect Capital InterNotes® | Unsecured Debt | February 15, 2025 – March 15, 2027 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	2.50%
Prospect Capital InterNotes® | Unsecured Debt | February 15, 2025 – March 15, 2027 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	7.25%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2026 – March 15, 2029
Debt Instrument [Line Items]
Tenor at Origination (in years)	5 years	5 years
Principal Outstanding	$ 123,488	$ 96,914
Weighted Average Interest Rate	4.17%	3.30%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2026 – March 15, 2029 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	2.25%	2.25%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2026 – March 15, 2029 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	7.75%	5.50%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2027 – November 15, 2029
Debt Instrument [Line Items]
Tenor at Origination (in years)	6 years
Principal Outstanding	$ 18,225
Weighted Average Interest Rate	3.54%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2027 – November 15, 2029 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	3.00%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2027 – November 15, 2029 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	6.25%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2028 – December 15, 2030
Debt Instrument [Line Items]
Tenor at Origination (in years)	7 years	7 years
Principal Outstanding	$ 34,601	$ 28,887
Weighted Average Interest Rate	4.05%	3.17%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2028 – December 15, 2030 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	2.75%	2.75%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2028 – December 15, 2030 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	8.00%	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	$ 3,226	$ 3,236
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 – March 15, 2034
Debt Instrument [Line Items]
Tenor at Origination (in years)	10 years
Principal Outstanding	$ 105,675
Weighted Average Interest Rate	4.91%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – March 15, 2034 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	3.15%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – March 15, 2034 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	8.00%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2033 – July 15, 2033
Debt Instrument [Line Items]
Tenor at Origination (in years)	12 years
Principal Outstanding	$ 13,773
Weighted Average Interest Rate	3.95%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2033 – July 15, 2033 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	3.70%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2033 – July 15, 2033 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	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	$ 14,109	$ 14,647
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	$ 2,959	$ 3,020
Weighted Average Interest Rate	4.82%	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	5.50%	5.00%
Prospect Capital InterNotes® | Unsecured Debt | November 15, 2032 – November 15, 2043
Debt Instrument [Line Items]
Tenor at Origination (in years)	20 years
Principal Outstanding	$ 3,864
Weighted Average Interest Rate	6.23%
Prospect Capital InterNotes® | Unsecured Debt | November 15, 2032 – November 15, 2043 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	5.75%
Prospect Capital InterNotes® | Unsecured Debt | November 15, 2032 – November 15, 2043 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	7.50%
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	$ 7,599	$ 7,800
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	$ 75,056	$ 79,042
Weighted Average Interest Rate	5.35%	5.31%
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%
Prospect Capital InterNotes® | Unsecured Debt | July 15, 2043 – November 15, 2043
Debt Instrument [Line Items]
Tenor at Origination (in years)	20 years	3 years
Principal Outstanding		$ 11,015
Weighted Average Interest Rate	6.58%	4.88%
Prospect Capital InterNotes® | Unsecured Debt | July 15, 2043 – November 15, 2043 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	6.50%	1.50%
Prospect Capital InterNotes® | Unsecured Debt | July 15, 2043 – November 15, 2043 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	7.50%	5.75%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2027 – June 15, 2029
Debt Instrument [Line Items]
Tenor at Origination (in years)		6 years	3 years
Principal Outstanding		$ 17,401
Weighted Average Interest Rate		3.41%	5.50%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2027 – June 15, 2029 | Minimum
Debt Instrument [Line Items]
Interest Rate Range		3.00%	5.00%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2027 – June 15, 2029 | Maximum
Debt Instrument [Line Items]
Interest Rate Range		6.00%	5.75%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – June 15, 2033
Debt Instrument [Line Items]
Tenor at Origination (in years)		10 years	5 years
Principal Outstanding		$ 79,944
Weighted Average Interest Rate		3.97%	4.50%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – June 15, 2033 | Minimum
Debt Instrument [Line Items]
Interest Rate Range		3.15%	4.50%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – June 15, 2033 | Maximum
Debt Instrument [Line Items]
Interest Rate Range		6.25%	5.50%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2033 – July 15, 2033
Debt Instrument [Line Items]
Tenor at Origination (in years)		12 years	6 years
Principal Outstanding		$ 14,241
Interest Rate Range			5.75%
Weighted Average Interest Rate		3.95%	5.75%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2033 – July 15, 2033 | Minimum
Debt Instrument [Line Items]
Interest Rate Range		3.70%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2033 – July 15, 2033 | Maximum
Debt Instrument [Line Items]
Interest Rate Range		4.00%
Prospect Capital InterNotes® | Unsecured Debt | November 15, 2032 – June 15, 2043
Debt Instrument [Line Items]
Tenor at Origination (in years)		20 years	10 years
Principal Outstanding		$ 1,958
Interest Rate Range			5.95%
Weighted Average Interest Rate		5.89%	5.95%
Prospect Capital InterNotes® | Unsecured Debt | November 15, 2032 – June 15, 2043 | Minimum
Debt Instrument [Line Items]
Interest Rate Range		5.75%
Prospect Capital InterNotes® | Unsecured Debt | November 15, 2032 – June 15, 2043 | Maximum
Debt Instrument [Line Items]
Interest Rate Range		6.50%