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Lease Agreement - Additional Information (Detail)	Apr. 30, 2016 USD ($)
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: