License and Collaboration Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended			12 Months Ended
	Dec. 31, 2019	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2019	May 07, 2019	Jul. 13, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payments and fees	$ 23,792	$ 20,415			$ 23,792
Revenue recognized		1,200		$ 1,200
Receivable from collaboration partner and contract asset - related party	6,755	$ 3,594			6,755
Transaction price	112,900				$ 112,900
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
Janssen Biotech, Inc. | License and Collaborative Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized		$ 3,600		1,600
Transaction price		$ 113,600
Development cost		80.00%
Increase (decrease) in transaction price		$ 700
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		$ 4,335		$ 1,564
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		18,300
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)
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		15,300
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
Janssen Biotech, Inc. | Pro Forma | First Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Former opt-in payments		125,000
Janssen Biotech, Inc. | Pro Forma | Second Opt-in Election
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Former opt-in payments		$ 200,000