Transactions with Controlled Companies - InterDent, Inc. (Details) - USD ($) $ in Thousands	3 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Jun. 30, 2022
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	$ 174,318	$ 146,271
Interest Receivable	18,781		$ 12,925
Other Receivables	$ 1,309		745
InterDent, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Contributed capital	100.00%
Reportable Legal Entities \| Subsidiaries \| InterDent, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	$ 7,508	6,328
Additions	0	7,778
Interest Income Capitalized as PIK	4,981	4,418
Repayment of Loan Receivable	0	123
Interest Receivable	86		80
Other Receivables	22		$ 16
Reportable Legal Entities \| Subsidiaries \| InterDent, Inc. \| Prospect Administration
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Managerial Assistance	$ 365	$ 0

Investment Company, Additional Investment

No definition available.

Name:	psec_InvestmentCompanyAdditionalInvestment
Namespace Prefix:	psec_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Investment Company, Contributed Capital

+ References

No definition available.

+ Details

Name:	psec_InvestmentCompanyContributedCapital
Namespace Prefix:	psec_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap-supplement_FeeIncome
Namespace Prefix:	us-gaap-supplement_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of interest capitalized during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

+ Details

Name:	us-gaap_InterestCostsCapitalized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of operating interest income, including, but not limited to, amortization and accretion of premiums and discounts on securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

+ Details

Name:	us-gaap_InterestIncomeOperating
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(a)(4))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Amount due from parties in nontrade transactions, classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(a)(4))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

The cash inflow associated with the collection, including prepayments, of loans receivable issued for financing of goods and services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromCollectionOfLoansReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Details

Name:	srt_OwnershipAxis=psec_InterDentIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=srt_ReportableLegalEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=psec_InterDentIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=psec_ProspectAdministrationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: