XML 32 R22.htm IDEA: XBRL DOCUMENT
v3.20.2

Fair Value (Tables) | 9 Months Ended
--- | ---
Sep. 30, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |
Summary of Change in Level 3 Warrant Liability Value | The following table summarizes the change in Level 3 warrant liability value (in thousands):
| Three Months Ended |  |  | Nine Months Ended |
Warrant liability | September 30, 2020 |  | September 30, 2019 |  |  | September 30, 2020 |  | September 30, 2019 |
Beginning balance | $ | 242 |  | $ | 424 |  |  | $ | 6,929 |  | $ | 916 |
Issuance |  | — |  |  | 10,215 |  |  |  | — |  |  | 10,215 |
Exercise/settlement |  | — |  |  | (794 | ) |  |  | — |  |  | (794 | )
Change in fair value |  | 81 |  |  | 561 |  |  |  | (2,342 | ) |  | 69 |
Reclassification to equity |  | (240 | ) |  | — |  |  |  | (4,504 | ) |  | — |
Ending balance | $ | 83 |  | $ | 10,406 |  |  | $ | 83 |  | $ | 10,406 |
Series T Warrants [Member] |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |
Schedule of Estimated Fair Value Determined Using Option Pricing Model Assumptions | The estimated fair value of the Series T Warrants as of September 30, 2020 and December 31, 2019 was determined by using an option pricing model with the following assumptions. The Series T Warrants will be marked to market as of each balance sheet date until they are exercised or upon expiration, with the changes in fair value recorded as non-operating income or loss in the statements of operations and comprehensive loss.
|  | As of September 30, 2020 |  |  | As of December 31, 2019 |
Expected term |  | 0.55 years |  |  | 1.1 years |
Common stock market price |  | $ | 2.56 |  |  | $ | 2.40 |
Risk-free interest rate |  |  | 0.11 | % |  |  | 1.59 | %
Expected volatility |  |  | 128 | % |  |  | 168 | %
Resulting fair value (per warrant) |  | $ | 1.04 |  |  | $ | 1.47 |
Series U Warrants [Member] |
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items] |
Schedule of Estimated Fair Value Determined Using Option Pricing Model Assumptions | The Company estimated the fair value of the Series U Warrants with the Black Scholes model with the following assumptions. The Series U Warrants that have not been amended (Note 11) will be marked to market as of each balance sheet date until they are exercised or upon expiration, with the changes in fair value recorded as non-operating income or loss in the statements of operations and comprehensive loss.
|  | As of September 30, 2020 |  |  | As of December 31, 2019 |
Expected term |  | 4 years |  |  | 4.75 years |
Common stock market price |  | $ | 2.56 |  |  | $ | 2.40 |
Risk-free interest rate |  |  | 0.22 | % |  |  | 1.68 | %
Expected volatility |  |  | 146 | % |  |  | 135 | %
Resulting fair value (per warrant) |  | $ | 2.21 |  |  | $ | 1.94 |

X
- Definition Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique used to measure similar asset in prior period by class of asset or liability on non-recurring basis. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueAssetsMeasuredOnNonrecurringBasisValuationTechniquesTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
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_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the fair value measurement of liabilities using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets), and gains or losses recognized in other comprehensive income (loss) and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs) by class of liability. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19279-110258 + Details
Name: | us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

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

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