XML 59 R27.htm IDEA: XBRL DOCUMENT
v3.20.1

Basis of Presentation and New Accounting Standards (Details) $ / shares in Units, $ in Millions | Aug. 06, 2019 shares | Aug. 05, 2019 $ / shares shares | Apr. 25, 2019 USD ($) | Apr. 24, 2019 USD ($) | Mar. 31, 2020 $ / shares shares | Dec. 31, 2019 $ / shares shares | Mar. 31, 2019 shares
--- | --- | --- | --- | --- | --- | --- | ---
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |
Reverse stock split effective date for trading purposes |  | Aug. 06, 2019 |  |  |  |  |
Reverse stock split of common stock |  | 0.02 |  |  |  |  |
Reverse stock split of common stock description |  | Upon effectiveness, each 50 shares of issued and outstanding common stock were converted into one newly issued and outstanding share of common stock |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  | $ 0.001 |  |  | $ 0.001 | $ 0.001 |
Common stock, shares issued (in shares) | shares | 50,000,000 | 50,000,000 |  |  | 3,880,588 | 3,880,588 |
Common stock, shares outstanding (in shares) | shares | 50,000,000 | 50,000,000 |  |  | 3,880,588 | 3,880,588 |
Preferred stock, shares authorized (in shares) | shares | 5,000,000 | 5,000,000 |  |  | 5,000,000 | 5,000,000 | 5,000,000
Common stock, reverse stock split, fractional shares issued | shares | 0 | 0 |  |  |  |  |
Sale of UK Subsidiary and Certain Assets [Member] | Loan and Security Agreement [Member] |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |
Cash proceeds from sale of subsidiary | $ |  |  |  | $ 4.0 |  |  |
Payments for principal, interest and fees | $ |  |  |  | $ 1.7 |  |  |
Sale of the Japanese Subsidiary and Certain Assets [Member] | Loan and Security Agreement [Member] |  |  |  |  |  |  |
Basis Of Presentation And New Accounting Standards [Line Items] |  |  |  |  |  |  |
Cash proceeds from sale of subsidiary | $ |  |  | $ 3.0 |  |  |  |
Payments for principal, interest and fees | $ |  |  | $ 1.4 |  |  |  |

X
- Definition Basis of presentation and new accounting standards line items. + References No definition available. + Details
Name: | pstv_BasisOfPresentationAndNewAccountingStandardsLineItems
Namespace Prefix: | pstv_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reverse stock split effective date for trading purposes. + References No definition available. + Details
Name: | pstv_ReverseStockSplitEffectiveDateForTradingPurposes
Namespace Prefix: | pstv_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Face amount or stated value per share of common stock. + 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 + Details
Name: | us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + 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 + Details
Name: | us-gaap_CommonStockSharesIssued
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation. + References Reference 1: 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 2: 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 + Details
Name: | us-gaap_CommonStockSharesOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition Cash payments for and related to principal collection on loans related to operating activities. + 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
Name: | us-gaap_PaymentsForLoans
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws. + 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(28)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_PreferredStockSharesAuthorized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the 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 12 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585 + Details
Name: | us-gaap_ProceedsFromDivestitureOfBusinesses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number of shares issued during the period as a result of a stock split. + 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(28)) -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 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 4: 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 + Details
Name: | us-gaap_StockIssuedDuringPeriodSharesStockSplits
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Description of the stock split arrangement. Also provide the retroactive effect given by a stock split that occurs after the balance date but before the release of financial statements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB Topic 4.C) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770 + Details
Name: | us-gaap_StockholdersEquityNoteStockSplit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SAB TOPIC 4.C) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770 + Details
Name: | us-gaap_StockholdersEquityNoteStockSplitConversionRatio1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DisposalGroupClassificationAxis=pstv_SaleOfUKSubsidiaryAndCertainAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=pstv_LoanAndSecurityAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DisposalGroupClassificationAxis=pstv_SaleOfJapaneseSubsidiaryAndCertainAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |