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CONSOLIDATED CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) (Parenthetical) - USD ($) | 3 Months Ended
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Jun. 30, 2021 | Mar. 31, 2021
Statement Of Stockholders Equity [Abstract] |  |
Offering cost, net | $ 17,000 | $ 100,000

X
- Definition Amount of sale of net of offering cost. + References No definition available. + Details
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Namespace Prefix: | pstv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_StatementOfStockholdersEquityAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration