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.

No definition available.

+ Details

Name:	ptgx_GovernmentProgramsLineItems
Namespace Prefix:	ptgx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of reduction of research and development expense in connection with the research and development tax incentive.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount as of the balance sheet date of amounts due under the terms of governmental, corporate, or foundation grants.

+ 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 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Carrying amount due within one year of the balance sheet date (or one operating cycle, if longer) from tax authorities as of the balance sheet date representing refunds of overpayments or recoveries based on agreed-upon resolutions of disputes.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.5(c))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3(a)(4))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	ptgx_RevenueSourceAxis=ptgx_SmallBusinessInnovationResearchGrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityNameAxis=us-gaap_AustralianTaxationOfficeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityAxis=ptgx_OverseasFindingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Government Programs (Details) $ in Thousands, $ in Millions	3 Months Ended			9 Months Ended
Government Programs (Details) $ in Thousands, $ in Millions	Sep. 30, 2019 USD ($)	Sep. 30, 2018 AUD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 AUD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 AUD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2018 AUD ($)	Dec. 31, 2018 USD ($)
Government Programs
Reduction of research and development expenses related to tax	$ 0	$ 0.4	$ 300			$ 1.6	$ 1,300
Research and development tax incentive receivable, net								$ 173		$ 1,429
SBIR Grant
Government Programs
Reduction of research and development expenses related to tax	$ 600		$ 200		$ 1,100		$ 400
Grants receivable								700		300
Australian
Government Programs
Reduction of research and development expenses related to tax				$ 1.8	$ 1,200
Overseas Findings \| Australian
Government Programs
Research and development tax incentive receivable, net				$ 0.3				$ 200	$ 2.0	$ 1,400