XML 77 R65.htm IDEA: XBRL DOCUMENT
v3.20.4

Stockholders' Equity - Common Stock (Details) - USD ($) |  |  |  |  |  |  | 2 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 17, 2021 | Oct. 23, 2020 | Oct. 02, 2020 | Sep. 30, 2020 | Jun. 16, 2020 | Sep. 21, 2018 | Feb. 17, 2021 | Dec. 31, 2018 | Sep. 30, 2020 | Dec. 31, 2020 | Dec. 31, 2019 | Mar. 16, 2020
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value |  |  |  |  |  |  |  |  |  |  | $ 2,208,000 |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  | $ 4,007,000 | 15,964,000 |
Sale/Issuance of common stock |  |  |  |  |  |  |  |  |  |  | $ 2,208,000 |
Common Stock [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  | 184,666 |
Common Stock [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value |  |  |  |  |  | $ 5,000,000 |  |  |  |  |  |
Period exercisable from the date of issuance |  |  |  |  |  | 24 months |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  |  | 32,170 |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  |  | $ 300,000 |
Remaining availability under financing facility |  |  |  |  |  |  |  |  |  | $ 0 |  |
Sale/Issuance of common stock |  |  |  |  |  | $ 5,000,000 |  |  |  |  |  |
Common Stock [Member] | Canaccord Genuity LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  | 1,616,331 |  |
Proceeds from sale of common stock |  | $ 10,000,000 |  |  |  |  |  |  |  | $ 3,200,000 |  |
Remaining availability under financing facility |  | 0 |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Canaccord Genuity LLC [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | 536,070 |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock | $ 1,500,000 |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Purchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  | 12,802 |  |  |  |
Proceeds from sale of common stock |  |  |  |  |  |  |  | $ 300,000 |  |  |  |
Common Stock [Member] | 2020 Repurchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value |  |  |  |  |  |  |  |  | $ 25,000,000 |  |  |
Period exercisable from the date of issuance |  |  |  |  |  |  |  |  | 36 months |  |  |
Common stock issued (in shares) |  |  | 180,701 |  |  |  |  |  | 0 | 353,113 |  |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  | $ 700,000 |  |
Sale/Issuance of common stock |  |  |  |  |  |  |  |  | $ 25,000,000 |  |  |
Closing price per share |  |  |  |  |  |  |  |  |  |  |  | $ 1.05
Fair value of commitment fee |  |  | $ 500,000 |  |  |  |  |  |  |  |  |
Common Stock [Member] | 2020 Repurchase Agreement [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) | 985,186 |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock | $ 2,900,000 |  |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | 2020 Repurchase Agreement [Member] | Commitment Fee |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  | 180,701 |  |
Common Stock [Member] | 2020 Repurchase Agreement [Member] | Minimum [Member] | Single Regular Purchase [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value |  |  |  | $ 500,000 |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  | 50,000 |  |  |  |  |  |  |  |
Sale/Issuance of common stock |  |  |  | $ 500,000 |  |  |  |  |  |  |  |
Common Stock [Member] | 2020 Repurchase Agreement [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  | 23,800,000 |  |  |  |  |  |  |
Percentage issuance of common stock |  |  |  |  | 19.99% |  |  |  |  |  |  |
Common Stock [Member] | 2020 Repurchase Agreement [Member] | Maximum [Member] | Single Regular Purchase [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  | 100,000 |  |  |  |  |  |  |  |
Closing price per share |  |  |  | $ 0.25 |  |  |  |  | $ 0.25 |  |  |
Common Stock [Member] | 2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued, value |  |  |  | $ 25,000,000 |  |  |  |  |  |  |  |
Period exercisable from the date of issuance |  |  |  | 36 months |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  |  |  |  | 353,113 |  |
Proceeds from sale of common stock |  |  |  |  |  |  |  |  |  | $ 700,000 |  |
Sale/Issuance of common stock |  |  |  | $ 25,000,000 |  |  |  |  |  |  |  |
Common Stock [Member] | 2020 Repurchase Agreement [Member] | Lincoln Park Capital Fund, LLC [Member] | Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued (in shares) |  |  |  |  |  |  | 985,186 |  |  |  |  |
Proceeds from sale of common stock |  |  |  |  |  |  | $ 2,900,000 |  |  |  |  |
Common Stock [Member] | Sales Agreement [Member] | Canaccord Genuity LLC [Member] | At The Market Offering Program [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Remaining availability under financing facility |  | 0 |  |  |  |  |  |  |  |  |  |
Common Stock [Member] | Sales Agreement [Member] | Canaccord Genuity LLC [Member] | Maximum [Member] | At The Market Offering Program [Member] |  |  |  |  |  |  |  |  |  |  |  |
Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sale of common stock |  | $ 10,000,000 |  |  |  |  |  |  |  |  |  |

X
- Definition Common Stock [Abstract] + References No definition available. + Details
Name: | pstv_CommonStockAbstract
Namespace Prefix: | pstv_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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: | num: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 Fair value portion of other assets. + References No definition available. + Details
Name: | us-gaap_OtherAssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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=121586364&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: | num:perShareItemType
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=109259400&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=109259400&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: | dei_LegalEntityAxis=pstv_LincolnParkCapitalFundLLCMember
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_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=pstv_PurchaseAgreementMember
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: | 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: | us-gaap_SubsidiarySaleOfStockAxis=pstv_AtTheMarketOfferingProgramMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |