Represents the percentage of details for PTG-200 provided to prescribers upon commercial launch.

No definition available.

Name:	ptgx_CollaborationAgreementDetailRequiredForCommercialLaunchPercent
Namespace Prefix:	ptgx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the penalty percentage for forfeiture of remaining rights and payment of cost.

+ References

No definition available.

+ Details

Name:	ptgx_CollaborationAgreementForfeitureOfRemainingRightsAndPaymentOfCostPenaltyPercentage
Namespace Prefix:	ptgx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the potential development, regulatory and sales milestone payments.

+ References

No definition available.

+ Details

Name:	ptgx_CollaborationArrangementPotentialDevelopmentRegulatoryAndSalesMilestonePayments
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of estimated variable consideration for cost-sharing payments for agreed upon services.

+ References

No definition available.

+ Details

Name:	ptgx_CollaborativeArrangementEstimatedVariableConsideration
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of future opt-in revenue eligible to receive.

+ References

No definition available.

+ Details

Name:	ptgx_CollaborativeArrangementFutureOptInRevenueEligibleToReceive
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the percentage of development cost incurred.

+ References

No definition available.

+ Details

Name:	ptgx_CollaborativeArrangementPercentageOfDevelopmentCostsIncurred
Namespace Prefix:	ptgx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the transaction price under the collaborative arrangements.

+ References

No definition available.

+ Details

Name:	ptgx_CollaborativeArrangementTransactionPrice
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of upfront payment to the entity under the arrangement.

+ References

No definition available.

+ Details

Name:	ptgx_CollaborativeArrangementUpfrontPayment
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Contingent Consideration Receivable

+ References

No definition available.

+ Details

Name:	ptgx_ContingentConsiderationReceivable
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Future Opt-In Payment Eligible To Receive Under Collaboration Arrangement.

+ References

No definition available.

+ Details

Name:	ptgx_FutureOptInPaymentEligibleToReceiveUnderCollaborationArrangement
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130549-203045

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84173487&loc=SL51747714-108306

+ Details

Name:	us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=82859839&loc=SL82860478-203043

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130539-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130545-203045

+ Details

Name:	us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_ProductOrServiceAxis=ptgx_LicenseAndCollaborativeRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_ProductOrServiceAxis=ptgx_FinancialServiceOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CounterpartyNameAxis=ptgx_JanssenBiotechIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

Janssen Collaboration Agreement (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Jul. 13, 2017	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price		$ 53,900		$ 53,900
Revenue recognized based on proportional performance		10,500
License and Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and collaboration revenue - related party		$ 10,781
Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost		20.00%
Phase 2 clinical trial \| Other services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and collaboration revenue - related party		$ 300
Janssen Biotech, Inc. \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront cash payment	$ 50,000
Development cost		80.00%
Estimated variable consideration for cost-sharing payments for agreed upon services			$ 3,900
Janssen Biotech, Inc. \| Forecast \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of details provided for PTG-200 to prescribers upon commercial launch			30.00%
Contingent consideration receivable upon filing of the IND			$ 25,000
Janssen Biotech, Inc. \| Forecast \| First Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Forfeiture of remaining rights and payment of cost, penalty percentage			50.00%
Future opt-in payment eligible to receive under collaboration arrangement			$ 125,000
Janssen Biotech, Inc. \| Forecast \| Second Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future opt-in revenue eligible to receive			200,000
Potential development, regulatory and sales milestone payments			$ 590,000