XML 48 R32.htm IDEA: XBRL DOCUMENT
v3.22.1

Stockholders' Equity - Common stock (Details) - USD ($) |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jan. 14, 2022 | Jun. 16, 2020 | Mar. 31, 2022 | Mar. 31, 2021 | Sep. 30, 2020 | Dec. 31, 2021 | Apr. 01, 2022 | Oct. 23, 2020
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Sale of common stock, net |  |  | $ 7,742,000 | $ 7,078,000 |  |  |  |
Proceeds from sale of common stock |  |  | 7,694,000 | 7,180,000 |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Sale of common stock, net |  |  | $ 6,000 | $ 2,000 |  |  |  |
Common stock issued (in shares) |  |  | 6,687,610 | 2,534,879 |  |  |  |
2020 Purchase 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) |  |  | 5,665,000 |  |  | 5,685,186 |  |
Period exercisable from the date of issuance |  |  |  |  | 36 months |  |  |
Closing price per share |  | $ 1.05 |  |  |  |  |  |
Proceeds from sale of common stock |  |  | $ 7,000,000.0 |  |  | $ 12,500,000 |  |
2020 Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Common Stock [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Remaining common stock issued and sold (in shares) |  |  |  |  |  |  | 0 |
2020 Purchase 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 Purchase 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 |  |  |  |  |  |
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 |  |  |  |  |  |  | $ 0
Sales Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] | Maximum [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] | Canaccord Genuity LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  | 1,022,610 |  |  |  |  |
Proceeds from sale of common stock |  |  | $ 700,000 |  |  |  |  |
2020 Distribution Agreement [Member] | Canaccord Genuity LLC [Member] | Common Stock [Member] |  |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  | 2,179,193 |  |
Proceeds from sale of common stock |  |  |  |  |  | $ 6,300,000 |  |

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_TwentyTwentyPurchaseAgreementMember
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: | srt_RangeAxis=srt_MinimumMember
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: |