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.

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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

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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.

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

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

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Fair Value and Maturity of Debt Outstanding - Schedule of Carrying Values and Estimated Fair Values of Debt Instruments (Details) - USD ($)	Sep. 30, 2022	Jun. 30, 2022	Sep. 30, 2021	Jun. 30, 2021	May 27, 2021	Jan. 22, 2021	Jun. 30, 2020	Jun. 30, 2019	Mar. 01, 2019	Dec. 05, 2018	Oct. 01, 2018	Jun. 30, 2018	Jun. 20, 2018	May 18, 2018	Jun. 30, 2017	Apr. 11, 2017	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2013	Mar. 15, 2013
Debt Instrument [Line Items]
Principal Outstanding	$ 2,670,175,000	$ 2,769,156,000
Net borrowings	2,640,020,000	2,737,276,000
Fair Value	$ 2,421,010,000	2,552,431,000
6.375% 2024 Notes
Debt Instrument [Line Items]
Stated rate	6.375%
3.364% 2026 Notes
Debt Instrument [Line Items]
Stated rate	3.364%
3.437% 2028 Notes
Debt Instrument [Line Items]
Stated rate	3.437%
Public Notes
Debt Instrument [Line Items]
Unamortized Discount & Debt Issuance Costs	$ 20,943,000	22,281,000
Prospect Capital InterNotes
Debt Instrument [Line Items]
Unamortized Discount & Debt Issuance Costs	6,969,000	7,122,000
Credit Facility
Debt Instrument [Line Items]
Net borrowings	799,851,000	839,464,000		$ 356,937,000			$ 237,536,000	$ 167,000,000				$ 37,000,000			$ 0		$ 0	$ 368,700,000	$ 92,000,000	$ 124,000,000
Credit Facility \| Revolving Credit Facility
Debt Instrument [Line Items]
Principal Outstanding	799,851,000	839,464,000
Unamortized Discount & Debt Issuance Costs	15,223,000	10,801,000
Net borrowings	799,851,000	839,464,000
Fair Value	$ 799,851,000	$ 839,464,000
Effective Interest Rate	2.05%	2.05%
Convertible Notes
Debt Instrument [Line Items]
Principal Outstanding	$ 156,168,000	$ 216,669,000
Unamortized Discount & Debt Issuance Costs	2,243,000	2,477,000
Net borrowings	153,925,000	214,192,000
Fair Value	154,919,000	218,847,000
Convertible Notes \| 2022 Notes
Debt Instrument [Line Items]
Stated rate														4.95%		4.95%
Principal Outstanding	0	60,501,000
Unamortized Discount & Debt Issuance Costs		18,000
Net borrowings		60,483,000
Fair Value		$ 60,753,000
Effective Interest Rate		5.63%
Convertible Notes \| 2025 Notes
Debt Instrument [Line Items]
Stated rate									6.375%
Principal Outstanding	156,168,000	$ 156,168,000
Unamortized Discount & Debt Issuance Costs	2,243,000	2,459,000
Net borrowings	153,925,000	153,709,000
Fair Value	$ 154,919,000	$ 158,094,000
Effective Interest Rate	6.63%	6.63%
Unsecured Debt \| 2023 Notes
Debt Instrument [Line Items]
Stated rate													5.875%								5.875%
Principal Outstanding	$ 283,872,000	$ 284,219,000
Unamortized Discount & Debt Issuance Costs	389,000	600,000
Net borrowings	283,483,000	283,619,000
Fair Value	$ 284,380,000	$ 286,101,000
Effective Interest Rate	6.07%	6.07%
Unsecured Debt \| 6.375% 2024 Notes
Debt Instrument [Line Items]
Stated rate	637.50%	637.50%									6.375%
Principal Outstanding	$ 81,240,000	$ 81,240,000
Unamortized Discount & Debt Issuance Costs	254,000	299,000
Net borrowings	80,986,000	80,941,000
Fair Value	$ 80,540,000	$ 82,084,000
Effective Interest Rate	6.57%	6.57%
Unsecured Debt \| 2026 Notes
Debt Instrument [Line Items]
Stated rate						3.706%				3.706%
Principal Outstanding	$ 400,000,000	$ 400,000,000
Unamortized Discount & Debt Issuance Costs	6,669,000	7,134,000
Net borrowings	393,331,000	392,866,000
Fair Value	$ 347,808,000	$ 355,316,000
Effective Interest Rate	3.98%	3.98%
Unsecured Debt \| 3.364% 2026 Notes
Debt Instrument [Line Items]
Stated rate	336.40%	336.40%			3.364%
Principal Outstanding	$ 300,000,000	$ 300,000,000
Unamortized Discount & Debt Issuance Costs	5,706,000	6,026,000
Net borrowings	294,294,000	293,974,000
Fair Value	$ 248,496,000	$ 254,931,000
Effective Interest Rate	3.60%	3.60%
Unsecured Debt \| 3.437% 2028 Notes
Debt Instrument [Line Items]
Stated rate	343.70%	343.70%	3.437%
Principal Outstanding	$ 300,000,000	$ 300,000,000
Unamortized Discount & Debt Issuance Costs	7,925,000	8,222,000
Net borrowings	292,075,000	291,778,000
Fair Value	$ 221,616,000	$ 229,866,000
Effective Interest Rate	3.64%	3.64%
Unsecured Debt \| Public Notes
Debt Instrument [Line Items]
Principal Outstanding	$ 1,365,112,000	$ 1,365,459,000
Net borrowings	1,344,169,000	1,343,178,000
Fair Value	1,182,840,000	1,208,298,000
Unsecured Debt \| Prospect Capital InterNotes
Debt Instrument [Line Items]
Principal Outstanding	349,044,000	347,564,000
Unamortized Discount & Debt Issuance Costs	6,969,000	7,122,000
Net borrowings	342,075,000	340,442,000
Fair Value	$ 283,400,000	$ 285,822,000
Effective Interest Rate	5.71%	5.71%