Additional payment obligation from the company to the former collaboration partner.

No definition available.

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Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

The aggregate amount of development milestone payment made by the entity.

+ References

No definition available.

+ Details

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

- Definition

The number of development milestone payments in collaboration agreement.

+ References

No definition available.

+ Details

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Namespace Prefix:	ptgx_
Data Type:	xbrli:integerItemType
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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

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- Definition

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Details

Name:	srt_ProductOrServiceAxis=ptgx_PhaseTwoBClinicalTrailOfPtg300Member
Namespace Prefix:
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Balance Type:
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- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
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- Details

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Data Type:	na
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Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
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- Details

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Research Collaboration and License Agreement (Details)	12 Months Ended
Research Collaboration and License Agreement (Details)	Dec. 31, 2020 USD ($) item	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Research Collaboration and License Agreement
Research and Development Expense	$ 74,506,000	$ 65,003,000	$ 59,497,000
Research Collaboration and License Agreement
Research Collaboration and License Agreement
Number of development milestone payments \| item	3
Aggregate development milestone payment	$ 1,000,000.0
Research and Development Expense	0	$ 0	$ 500,000
Research Collaboration and License Agreement \| Phase 2b \| Minimum \| Entity Required to Continue to Make Payments
Research Collaboration and License Agreement
Additional payment obligation to the former collaboration partner	1,000,000.0
Research Collaboration and License Agreement \| Phase 2b \| Maximum \| Entity Required to Continue to Make Payments
Research Collaboration and License Agreement
Additional payment obligation to the former collaboration partner	3,000,000.0
Research Collaboration and License Agreement \| Phase 3 \| Minimum \| Entity Required to Continue to Make Payments
Research Collaboration and License Agreement
Additional payment obligation to the former collaboration partner	1,500,000
Research Collaboration and License Agreement \| Phase 3 \| Maximum \| Entity Required to Continue to Make Payments
Research Collaboration and License Agreement
Additional payment obligation to the former collaboration partner	$ 4,500,000