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 decrease in transaction price under the collaborative arrangements.

+ References

No definition available.

+ Details

Name:	ptgx_CollaborativeArrangementDecreaseInTransactionPrice
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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 fee and financial service revenue classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Definition

The amount of consideration recognized during the period for the milestone or milestones.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 28
-Section 50
-Paragraph 2
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=68058744&loc=SL6892177-166501

+ Details

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

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130556-203045

+ Details

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

- Details

Name:	us-gaap_TypeOfArrangementAxis=us-gaap_CollaborativeArrangementProductAgreementMember
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_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_PhaseTwoClinicalTrialMember
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 License and Collaboration Agreement (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Jul. 13, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price		$ 54.3
Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost				20.00%
License and collaboration revenue				$ 20.1
First Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future opt-in revenue eligible to receive				125.0
Janssen biotech \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront cash payment	$ 50.0			$ 50.0
Development cost				80.00%
Transaction price				$ 53.9
Decrease in transaction price				0.4
Estimated variable consideration for cost-sharing payments for agreed upon services				3.9
License and collaboration revenue				19.0
Transaction price based on proportional performance				19.0
other services				$ 1.1
Janssen biotech \| 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			$ 25.0
Janssen biotech \| Forecast \| Phase 2 clinical trial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future opt-in revenue eligible to receive			$ 25.0
Janssen biotech \| 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			$ 125.0
Janssen biotech \| Forecast \| Second Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future opt-in revenue eligible to receive			200.0
Potential development, regulatory and sales milestone payments			$ 590.0