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v3.7.0.1

Subsequent Events - Additional Information (Detail) - USD ($) | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Mar. 31, 2017
Subsequent Event [Line Items] |  |
Lease commencement date | Jul. 01, 2017 |
Lease expiration date | Jun. 30, 2024 |
Aggregate minimum lease payments | $ 455,000 |
Security deposit | $ 30,000 |
Subsequent Event [Member] |  |
Subsequent Event [Line Items] |  |
Aggregate minimum lease payments |  | $ 13,400,000
Security deposit |  | $ 450,000

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- Definition Operating leases commencement date. + References No definition available. + Details
Name: | ptgx_OperatingLeasesCommencementDate
Namespace Prefix: | ptgx_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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- Definition Date which lease or group of leases is set to expire, in CCYY-MM-DD format. + References No definition available. + Details
Name: | us-gaap_LeaseExpirationDate1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsDue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The amount of an asset, typically cash, provided to a counterparty to provide certain assurance of performance by the entity pursuant to the terms of a written or oral agreement, such as a lease. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.8,17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_SecurityDeposit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |