XML 14 R44.htm IDEA: XBRL DOCUMENT
v3.20.1

Stockholders' Equity - Warrants (Details) - USD ($) |  |  | 3 Months Ended
--- | --- | --- | ---
Jul. 25, 2018 | Jul. 17, 2018 | Mar. 31, 2020 | Mar. 31, 2019
Series U Warrants [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Common stock issued (in shares) |  |  | 3,450,000 |
Sale of Stock, Price Per Share |  |  | $ 5.00 |
Warrants expected term |  |  | 5 years |
Representative Warrants [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Number of shares callable by warrants (in shares) |  |  | 75,000 |
Warrant exercise price (in dollars per share) |  |  | $ 6.25 |
Common Stock [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Common stock issued (in shares) |  |  |  | 139,855,000
Warrants expected term |  |  | 5 years |
Series C Convertible Preferred Stock [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Conversion Price Per Share | $ 7.50 |  |  |
Preferred stock conversion price reduced (in dollars per share) | $ 3.2132 |  |  |
Common Class A |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Common stock issued (in shares) |  |  | 289,000 |
Common Class B |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Number of shares callable by warrants (in shares) |  |  | 2,711,000 |
2018 Rights Offering [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Number of shares callable by warrants (in shares) |  | 1 |  |
Common stock issued (in shares) | 6,723 |  |  |
Gross proceeds from private placement of stock | $ 5,700,000 |  |  |
2018 Rights Offering [Member] | Outstanding Warrants [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Number of shares callable by warrants (in shares) |  | 1,050 |  |
Warrant exercise price (in dollars per share) |  | $ 1,000 |  |
2018 Rights Offering [Member] | Common Stock and Series B Convertible Preferred Stock [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Charge on Non Transferable Subscription Rights |  | $ 0 |  |
2018 Rights Offering [Member] | Series C Convertible Preferred Stock [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Number of shares callable by warrants (in shares) |  | 20,000 |  |
Series T Warrants [Member] | 2018 Rights Offering [Member] | Outstanding Warrants [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Class of warrant outstanding |  |  | 3,788,400 |
Number of warrants exercised |  |  | 75,768 |
Series U Warrants [Member] | Outstanding Warrants [Member] |  |  |  |
Class Of Stock [Line Items] |  |  |  |
Class of warrant outstanding |  |  | 3,525,000 |
Number of warrants exercised |  |  | 3,525,000 |

X
- Definition Charge on non-transferable subscription rights. + References No definition available. + Details
Name: | pstv_ChargeOnNonTransferableSubscriptionRights
Namespace Prefix: | pstv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Conversion price per share. + References No definition available. + Details
Name: | pstv_ConversionPricePerShare
Namespace Prefix: | pstv_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Gross proceeds from issuance of private placement. + References No definition available. + Details
Name: | pstv_GrossProceedsFromIssuanceOfPrivatePlacement
Namespace Prefix: | pstv_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number of warrants exercised + References No definition available. + Details
Name: | pstv_NumberOfWarrantsExercised
Namespace Prefix: | pstv_
Data Type: | xbrli:sharesItemType
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 Exercise price per share or per unit of warrants or rights outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)(4)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
Name: | us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)(2)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
Name: | us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of warrants or rights outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(i)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
Name: | us-gaap_ClassOfWarrantOrRightOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Per share decrease in conversion price of convertible preferred stock. Excludes change due to standard antidilution provision. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 + Details
Name: | us-gaap_PreferredStockConvertibleConversionPriceDecrease
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction. + References No definition available. + Details
Name: | us-gaap_SaleOfStockPricePerShare
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=6877327&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=27012166&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=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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_StatementEquityComponentsAxis=pstv_RepresentativeSeriesUWarrantMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=pstv_SeriesCConvertiblePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassBMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ClassOfWarrantOrRightAxis=pstv_TwoThousandEighteenRightsOfferingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=pstv_CommonStockAndSeriesBConvertiblePreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ClassOfWarrantOrRightAxis=pstv_SeriesTWarrantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementClassOfStockAxis=pstv_TwoThousandEighteenRightsOfferingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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