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

Amount of operating dividend income on securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.2)
-URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

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

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

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

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

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

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

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

Percentage investment held by members or limited partners of limited liability company (LLC) or limited partnership (LP).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPMembersOrLimitedPartnersOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Amount of revenue and income classified as other.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.4)
-URI https://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

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

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

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

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

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

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

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

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.

No definition available.

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

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

Name:	srt_TitleOfIndividualAxis=psec_MembersOfValleyElectricCompanyIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

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

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

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

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

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

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

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

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

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

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

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