Revolving Credit Facility - Narrative (Details) - USD ($)		3 Months Ended		12 Months Ended
	Sep. 15, 2022	Sep. 30, 2022	Sep. 30, 2021	Jun. 30, 2022
Line of Credit Facility [Line Items]
Credit facility outstanding balance		$ 799,851,000		$ 839,464,000
Percentage of total assets at fair value		100.00%		100.00%
Debt financing costs		$ 15,223,000		$ 10,801,000
Investments Held Benchmark | Net Assets | Affiliated Entity | Prospect Capital Funding LLC
Line of Credit Facility [Line Items]
Percentage of total assets at fair value		35.10%
Revolving Credit Facility | Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 1,634,000,000
Accordion feature, increase limit		2,000,000,000
Remaining borrowing capacity		659,623,000		660,536,000
Credit facility outstanding balance		799,851,000		839,464,000
Collateralized financings		2,675,968,000
Debt issuance costs, gross		23,857,000
Debt financing costs		15,223,000		$ 10,801,000
Interest expense		$ 11,726,000	$ 4,569,000
Revolving Credit Facility | More than 60% Drawn | Credit Facility
Line of Credit Facility [Line Items]
Unused capacity fee rate	0.40%
Revolving Credit Facility | More Than 35% and An Amount Less Than or Equal to 60% | Credit Facility
Line of Credit Facility [Line Items]
Unused capacity fee rate	0.70%
Revolving Credit Facility | Less Than 35% or Equal to 35% | Credit Facility
Line of Credit Facility [Line Items]
Unused capacity fee rate	1.50%
Revolving Credit Facility | SOFR | Credit Facility
Line of Credit Facility [Line Items]
Basis spread	2.05%