Number of Integrin research targets.

No definition available.

Name:	plrx_NumberOfIntegrinResearchTargets
Namespace Prefix:	plrx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of outstanding shares on fully diluted basis.

+ References

No definition available.

+ Details

Name:	plrx_PercentageOfOutstandingSharesOnFullyDilutedBasis
Namespace Prefix:	plrx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Share based compensation arrangement by share based payment award options grants in period fair value.

+ References

No definition available.

+ Details

Name:	plrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodFairValue
Namespace Prefix:	plrx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

+ Details

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

- Details

Name:	us-gaap_TypeOfArrangementAxis=plrx_NovartisAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=plrx_NovartisMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=us-gaap_IPOMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_EmployeeStockOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=plrx_ThirdRockVenturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=plrx_NonemployeeDirectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Party Transactions (Details)	1 Months Ended			6 Months Ended
Related Party Transactions (Details)	Jun. 30, 2020 USD ($) shares	Mar. 31, 2020 USD ($) shares	Oct. 31, 2019 USD ($) class	Jun. 30, 2021	Dec. 31, 2020
Novartis Agreement \| Novartis
Related Party Transaction [Line Items]
Number of Integrin research targets (up to) \| class			3
Committed to provide equity financing (up to)			$ 30,000,000.0
Percentage of outstanding equity on fully diluted basis				6.00%	6.10%
IPO \| Novartis Agreement \| Novartis
Related Party Transaction [Line Items]
Committed to provide equity financing (up to)			10,000,000.0
Series C Redeemable Convertible Preferred Stock \| Novartis Agreement \| Novartis
Related Party Transaction [Line Items]
Committed to provide equity financing (up to)			$ 20,000,000.0
Stock Options
Related Party Transaction [Line Items]
Options granted (in shares) \| shares	26,572
Grant date fair value of stock option	$ 500,000
Vesting rights percentage	25.00%
Third Rock Ventures \| Non-employee Director \| Stock Options
Related Party Transaction [Line Items]
Options granted (in shares) \| shares		26,573
Grant date fair value of stock option		$ 100,000
Vesting rights percentage				8.3333%
Vesting period				3 years