Marketable Securities - Schedule of Marketable Securities (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Marketable Securities [Line Items]
Marketable securities, Amortized cost	$ 260,116
Marketable securities, Gross unrealized gain	2
Marketable securities, Gross unrealized loss	(713)
Marketable securities, Fair value	259,405
Corporate Debt Securities
Marketable Securities [Line Items]
Marketable securities, Amortized cost	193,798
Marketable securities, Gross unrealized gain	1
Marketable securities, Gross unrealized loss	(696)
Marketable securities, Fair value	193,103
Commercial Paper
Marketable Securities [Line Items]
Marketable securities, Amortized cost	66,318
Marketable securities, Gross unrealized gain	1
Marketable securities, Gross unrealized loss	(17)
Marketable securities, Fair value	$ 66,302

Available for sale debt securities accumulated gross unrealized gain net of tax.

No definition available.

Name:	prld_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainNetOfTax
Namespace Prefix:	prld_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Available for sale debt securities accumulated gross unrealized loss net of tax.

+ References

No definition available.

+ Details

Name:	prld_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossNetOfTax
Namespace Prefix:	prld_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124260329&loc=d3e26626-111562

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_MarketableSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: