XML 48 R36.htm IDEA: XBRL DOCUMENT
v3.20.4

Fair Value - Schedule of Estimated Fair Value Determined Using Option Pricing Model Assumptions (Details) - $ / shares | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Series U Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants expected term | 5 years |
Level 3 [Member] | Expected Term [Member] | Series T Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants expected term | 1 month 6 days | 1 year 1 month 6 days
Level 3 [Member] | Expected Term [Member] | Series U Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants expected term | 3 years 9 months | 4 years 9 months
Level 3 [Member] | Common Stock Market Price [Member] | Series T Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants measurement input | 2.02 | 2.40
Level 3 [Member] | Common Stock Market Price [Member] | Series U Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants measurement input | 2.02 | 2.40
Level 3 [Member] | Risk-free Interest Rate [Member] | Series T Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants measurement input | 0.08 | 1.59
Level 3 [Member] | Risk-free Interest Rate [Member] | Series U Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants measurement input | 0.24 | 1.68
Level 3 [Member] | Expected Volatility [Member] | Series T Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants measurement input | 57 | 168
Level 3 [Member] | Expected Volatility [Member] | Series U Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants measurement input | 149.0 | 134.5
Level 3 [Member] | Resulting Fair Value (Per Warrant) [Member] | Series T Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants measurement input | 0.05 | 1.47
Level 3 [Member] | Resulting Fair Value (Per Warrant) [Member] | Series U Warrants [Member] |  |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |  |
Warrants measurement input | 1.56 | 1.94

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

X
- Definition Value of input used to measure outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_WarrantsAndRightsOutstandingMeasurementInput
Namespace Prefix: | us-gaap_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Period between issuance and expiration of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_WarrantsAndRightsOutstandingTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=pstv_SeriesUWarrantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputExpectedTermMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=pstv_SeriesTWarrantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputSharePriceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputRiskFreeInterestRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputPriceVolatilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MeasurementInputTypeAxis=pstv_MeasurementInputResultingFairValuePerWarrantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |