License and Collaboration Agreement (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	May 07, 2019	Dec. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Mar. 31, 2020	Jul. 13, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payments and fees		$ 23,792	$ 16,784		$ 16,784		$ 23,792
Revenue recognized			2,100		3,300
Receivable from collaboration partner and contract asset - related party		6,755	2,997		$ 2,997		$ 6,755
Transaction price								$ 113,600
License and Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost							20.00%
Second-Generation Analog, Phase 3 CD Clinical Trial Primary Clinical Endpoint [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost					80.00%
Second Generation Analog Phase 2 Cd Clinical Trial Primary Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost					80.00%
First Amendment | Development, regulatory and sales milestone payments
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Eligible payment receivable	$ 1,000,000
First Amendment | Development, regulatory and sales milestone payments | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentages on net product sales	10.00%
Janssen Biotech, Inc. | License and Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized			5,700		$ 9,400
Transaction price			113,900		$ 113,900
Development cost					80.00%
Increase (decrease) in transaction price					$ 300
Janssen Biotech, Inc. | Additional services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue			$ 500	$ 0	$ 500	$ 0
Janssen Biotech, Inc. | Second-Generation Analog, Phase 3 CD Clinical Trial Primary Clinical Endpoint [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost					20.00%
Janssen Biotech, Inc. | License and Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price recognized based on proportional performance					$ 10,493	1,182
Janssen Biotech, Inc. | License and Collaboration Agreement | Upfront cash payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payments and fees									$ 50,000
Janssen Biotech, Inc. | First, second-generation compound | Milestone payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount payable upon the effectiveness of the First Amendment							$ 7,500
Janssen Biotech, Inc. | First, second-generation compound | Second-Generation Analog, Phase 3 CD Clinical Trial Primary Clinical Endpoint [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research program cost					100.00%
Janssen Biotech, Inc. | Second and third, second-generation compounds | Second-Generation Analog, Phase 3 CD Clinical Trial Primary Clinical Endpoint [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research program cost					50.00%
Janssen Biotech, Inc. | Thereafter | Second-Generation Analog, Phase 3 CD Clinical Trial Primary Clinical Endpoint [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research program cost					100.00%
Janssen Biotech, Inc. | Second-Generation Phase 2b Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount payable upon the effectiveness of the First Amendment		$ 5,000
Janssen Biotech, Inc. | Second-Generation Phase 2b Milestone | Milestone payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized					$ 7,500
Janssen Biotech, Inc. | Phase 2 clinical trial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount payable upon the effectiveness of the First Amendment					50,000
Janssen Biotech, Inc. | Phase 2 clinical trial | License and Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue					18,400
Janssen Biotech, Inc. | Phase 2 clinical trial | Second-Generation Analog, Phase 3 CD Clinical Trial Primary Clinical Endpoint [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost				20.00%
Janssen Biotech, Inc. | First Amendment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized					5,000
Increase (decrease) in transaction price				$ 9,400		$ 9,400	$ (9,400)
Janssen Biotech, Inc. | First Amendment | License and Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized				25,000
Janssen Biotech, Inc. | First Amendment | PTG-200, Phase 3 CD Clinical Trial Primary Clinical Endpoint
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Eligible payment receivable	$ 100,000
Janssen Biotech, Inc. | First Amendment | Second-Generation Analog, Phase 3 CD Clinical Trial Primary Clinical Endpoint [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount payable upon the effectiveness of the First Amendment					50,000
Eligible payment receivable	$ 115,000
Janssen Biotech, Inc. | Amended First Opt-in | Upfront cash payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount payable upon the effectiveness of the First Amendment					50,000
Janssen Biotech, Inc. | Amended Second Opt-in | Upfront cash payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount payable upon the effectiveness of the First Amendment					50,000
Janssen Biotech, Inc. | Estimated variable consideration | License and Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue					$ 15,500
Janssen Biotech, Inc. | Pro Forma | License and Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized				25,000
Janssen Biotech, Inc. | Pro Forma | Milestone payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized				$ 25,000