Prospect Capital InterNotes® - Schedule of Notes Outstanding (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Principal Outstanding	$ 2,294,376	$ 2,454,992
Net Carrying Value	2,273,716	2,433,911
Prospect Capital InterNotes®
Debt Instrument [Line Items]
Unamortized debt issuance	(9,040)	(7,999)
Prospect Capital InterNotes® | Unsecured Debt
Debt Instrument [Line Items]
Principal Outstanding	603,262	504,028
Unamortized debt issuance	(9,040)	(7,999)
Net Carrying Value	$ 594,222	$ 496,029
Weighted Average Interest Rate	7.14%		6.17%
Prospect Capital InterNotes® | Unsecured Debt | Minimum
Debt Instrument [Line Items]
Interest Rate Range	6.50%		5.75%
Prospect Capital InterNotes® | Unsecured Debt | Maximum
Debt Instrument [Line Items]
Interest Rate Range	7.50%		6.50%
Prospect Capital InterNotes® | Unsecured Debt | February 15, 2025 – October 15, 2027
Debt Instrument [Line Items]
Tenor at Origination (in years)	3 years
Principal Outstanding	$ 103,588
Weighted Average Interest Rate	6.64%
Prospect Capital InterNotes® | Unsecured Debt | February 15, 2025 – October 15, 2027 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	2.50%
Prospect Capital InterNotes® | Unsecured Debt | February 15, 2025 – October 15, 2027 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	7.25%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2026 – October 15, 2029
Debt Instrument [Line Items]
Tenor at Origination (in years)	5 years	5 years
Principal Outstanding	$ 175,054	$ 143,554
Weighted Average Interest Rate	5.06%	4.60%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2026 – October 15, 2029 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	2.25%	2.25%
Prospect Capital InterNotes® | Unsecured Debt | January 15, 2026 – October 15, 2029 | Maximum
Debt Instrument [Line Items]
Interest Rate Range	7.75%	7.75%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2027 – November 15, 2029
Debt Instrument [Line Items]
Tenor at Origination (in years)	6 years
Principal Outstanding	$ 18,348
Weighted Average Interest Rate	3.56%
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	$ 34,508	$ 34,601
Weighted Average Interest Rate	4.06%	4.05%
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%	8.00%
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	$ 3,215	$ 3,215
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 – October 15, 2034
Debt Instrument [Line Items]
Tenor at Origination (in years)	10 years
Principal Outstanding	$ 153,540
Weighted Average Interest Rate	5.73%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – October 15, 2034 | Minimum
Debt Instrument [Line Items]
Interest Rate Range	3.15%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – October 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	$ 13,626
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	$ 13,808	$ 14,016
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	$ 2,949	$ 2,949
Weighted Average Interest Rate	4.82%	4.82%
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%	5.50%
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	$ 7,494	$ 7,494
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	$ 73,268	$ 74,323
Weighted Average Interest Rate	5.36%	5.34%
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 | 0
Debt Instrument [Line Items]
Tenor at Origination (in years)		3 years
Principal Outstanding		$ 64,439
Weighted Average Interest Rate		6.46%
Prospect Capital InterNotes® | Unsecured Debt | 0 | Minimum
Debt Instrument [Line Items]
Interest Rate Range		2.50%
Prospect Capital InterNotes® | Unsecured Debt | 0 | Maximum
Debt Instrument [Line Items]
Interest Rate Range		7.25%
Prospect Capital InterNotes® | Unsecured Debt | June 15, 2027 – November 15, 2029
Debt Instrument [Line Items]
Tenor at Origination (in years)		6 years
Principal Outstanding		$ 18,348
Weighted Average Interest Rate		3.56%
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 | August 15, 2029 – June 15, 2034
Debt Instrument [Line Items]
Tenor at Origination (in years)		10 years
Principal Outstanding		$ 123,477
Weighted Average Interest Rate		5.30%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – June 15, 2034 | Minimum
Debt Instrument [Line Items]
Interest Rate Range		3.15%
Prospect Capital InterNotes® | Unsecured Debt | August 15, 2029 – June 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		$ 13,748
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 | 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%