Debt - Minimum future payment obligations including principal and final payment fee (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Debt
2021	$ 833
2022	5,000
2023	4,452
Total	$ 10,285

The amount of long-term debt principal payable and final payment fee maturing in the fourth fiscal year following the latest fiscal year.

No definition available.

Name:	ptgx_LongTermDebtAndFinalPaymentFeeMaturitiesRepaymentsOfPrincipalInYearFour
Namespace Prefix:	ptgx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant