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NanoTx License Agreement - Additional Information (Details) - NanoTx License Agreement [Member] | Mar. 29, 2020 USD ($)
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License fee payment in cash | $ 400,000
License fee payment in common stock | 300,000
Development and Sales Milestone [Member] |
Milestone payments | $ 136,500,000

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Namespace Prefix: | pstv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Stock issued during period, value, license. + References No definition available. + Details
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Namespace Prefix: | pstv_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The amount of cash paid for royalties during the current period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3536-108585 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | credit
Period Type: | duration

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- Details
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |