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Lease Agreement - Additional Information (Detail) | Apr. 30, 2016 USD ($)
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Lease Agreements [Member] | Milpitas [Member] |
Leases [Line Items] |
Additional lease payments | $ 80,000

X
- Definition Additional lease rent payable. + References No definition available. + Details
Name: | ptgx_AdditionalLeaseRentPayable
Namespace Prefix: | ptgx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Leases. + References No definition available. + Details
Name: | ptgx_LeasesLineItems
Namespace Prefix: | ptgx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_LeaseAgreementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementGeographicalAxis=ptgx_MilpitasMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |