XML 52 R42.htm IDEA: XBRL DOCUMENT v3.20.2

Stockholders' Equity - Preferred Stock (Details) - $ / shares	1 Months Ended	6 Months Ended		12 Months Ended
	Apr. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Aug. 06, 2019	Aug. 05, 2019
Preferred Stock [Abstract]
Preferred stock, shares authorized (in shares)		5,000,000		5,000,000	5,000,000	5,000,000
Preferred stock, par value (in dollars per share)		$ 0.001		$ 0.001
Preferred stock, shares outstanding (in shares)		1,959		1,959
Preferred stock, shares outstanding (in shares)		1,959		1,959
Series A Convertible Preferred Stock [Member]
Preferred Stock [Abstract]
Preferred stock, shares outstanding (in shares)		0		0
Convertible preferred stock		3.60%		3.60%
Preferred stock, shares outstanding (in shares)		0		0
Series B Convertible Preferred Stock [Member]
Preferred Stock [Abstract]
Preferred stock, shares outstanding (in shares)		1,021		1,021
Preferred stock, shares outstanding (in shares)		1,021		1,021
Series B Convertible Preferred Stock [Member] | 2018 Rights Offering [Member]
Preferred Stock [Abstract]
Preferred stock, shares outstanding (in shares)		1,021
Preferred stock, shares outstanding (in shares)		1,021
Number of preferred stock, shares converted			6,133
Series C Convertible Preferred Stock [Member]
Preferred Stock [Abstract]
Preferred stock, shares outstanding (in shares)		938		938
Preferred stock, shares outstanding (in shares)		938		938
Conversion Price Per Share	$ 3.2132
Preferred stock conversion price reduced (in dollars per share)	$ 2.25
Series C Convertible Preferred Stock [Member] | 2018 Rights Offering [Member]
Preferred Stock [Abstract]
Preferred stock, shares outstanding (in shares)		938
Preferred stock, shares outstanding (in shares)		938
Number of preferred stock, shares converted			291,920

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

Number Of Preferred Stock Shares Exercised.

+ References

No definition available.

+ Details

Name:	pstv_NumberOfPreferredStockSharesExercised
Namespace Prefix:	pstv_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Preferred Stock [Abstract]

+ References

No definition available.

+ Details

Name:	pstv_PreferredStockAbstract
Namespace Prefix:	pstv_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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

The percentage rate used to calculate dividend payments on preferred stock.

+ References

No definition available.

+ Details

Name:	us-gaap_PreferredStockDividendRatePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

+ 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_PreferredStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

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

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

+ 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_PreferredStockSharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=pstv_SeriesAConvertiblePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=pstv_SeriesBConvertiblePreferredStockMember
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_StatementClassOfStockAxis=pstv_SeriesCConvertiblePreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: