XML 69 R57.htm IDEA: XBRL DOCUMENT v3.22.0.1

Stockholders' Equity - Common stock (Details) - USD ($)						9 Months Ended	12 Months Ended
	Feb. 24, 2022	Jan. 14, 2022	Jan. 01, 2022	Sep. 30, 2020	Jun. 16, 2020	Sep. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Oct. 23, 2020
Class of Stock [Line Items]
Sale of common stock, net							$ 18,581,000	$ 3,882,000
Proceeds from sale of common stock							18,675,000	4,007,000
Common Stock [Member]
Class of Stock [Line Items]
Sale of common stock, net							$ 8,000	$ 2,000
Common stock issued (in shares)							7,864,379	2,150,113
2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member]
Class of Stock [Line Items]
Sale of common stock, net						$ 25,000,000.0
Common stock issued (in shares)							5,685,186	353,113
Period exercisable from the date of issuance						36 months
Closing price per share					$ 1.05
Proceeds from sale of common stock							$ 12,500,000	$ 700,000
2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Common stock issued (in shares)			5,665,000
Proceeds from sale of common stock			$ 7,000,000.0
Remaining common stock issued and sold (in shares)			0
2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Commitment Fee [Member]
Class of Stock [Line Items]
Common stock issued (in shares)								180,701
2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Minimum [Member]
Class of Stock [Line Items]
Percentage issuance of common stock					19.99%
2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Minimum [Member] | Single Regular Purchase [Member]
Class of Stock [Line Items]
Sale of common stock, net				$ 500,000
Common stock issued (in shares)				50,000
2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Maximum [Member]
Class of Stock [Line Items]
Common stock issued (in shares)					23,800,000
2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Maximum [Member] | Single Regular Purchase [Member]
Class of Stock [Line Items]
Common stock issued (in shares)				100,000
Closing price per share				$ 0.25		$ 0.25
Sales Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | At The Market Offering Program [Member]
Class of Stock [Line Items]
Remaining availability under financing facility									$ 0
Sales Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Subsequent Event [Member] | At The Market Offering Program [Member]
Class of Stock [Line Items]
Remaining availability under financing facility		$ 0
Sales Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Maximum [Member] | Subsequent Event [Member] | At The Market Offering Program [Member]
Class of Stock [Line Items]
Proceeds from sale of common stock		$ 5,000,000
2022 Distribution Agreement [Member] | Common Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Common stock issued (in shares)	1,000,000
Proceeds from sale of common stock	$ 900,000
2022 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Common stock issued (in shares)			1,000,000
Proceeds from sale of common stock			$ 900,000
2020 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member]
Class of Stock [Line Items]
Common stock issued (in shares)							2,179,193	1,616,331
Proceeds from sale of common stock							$ 6,300,000	$ 3,200,000
Remaining availability under financing facility							$ 0

X

- Definition

Common stock, sales, available for issuance.

+ References

No definition available.

+ Details

Name:	pstv_CommonStockSalesAvailableForIssuance
Namespace Prefix:	pstv_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Percentage issuance of common stock.

+ References

No definition available.

+ Details

Name:	pstv_PercentageIssuanceOfCommonStock
Namespace Prefix:	pstv_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Refers to the period exercisable from the date of issuance.

+ References

No definition available.

+ Details

Name:	pstv_PeriodExercisableFromTheDateOfIssuance
Namespace Prefix:	pstv_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

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

X

- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585

+ Details

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

X

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of shares of stock issued as of the balance sheet date, including shares that had been issued and were previously outstanding but which are now held in the treasury.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21463-112644

+ Details

Name:	us-gaap_SharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Number of new stock issued during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21463-112644

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123467817&loc=d3e21463-112644

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

X

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=pstv_TwentyTwentyRepurchaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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

X

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=pstv_CommitmentFeeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_SingleStockFutureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=pstv_SalesAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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

X

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=pstv_AtTheMarketOfferingProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=pstv_TwoThousandTwentyTwoDistributionAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=pstv_DistributionAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: