License and Collaboration Agreement (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 07, 2019	Jul. 13, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payments and fees	$ 23,792	$ 23,792								$ 23,792
Revenue		2,719	$ 4,141		$ 1,560	$ 2,353	$ 6,117	$ 11,674	$ 10,781
Revenue recognized										1,600	$ 23,500	$ 0
Receivable from collaboration partner and contract asset - related party	6,755	6,755				4,587				$ 6,755	4,587
Transaction price						$ 60,700					60,700	53,900
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%
Phase 2 clinical trial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost										80.00%
Phase 2 clinical trial | Other services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue											100	1,100
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										$ 200	30,900	20,100
Increase (decrease) in transaction price					$ 1,600					$ (9,400)
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]
Revenue											30,800
Transaction price recognized based on proportional performance										$ 9,149	30,825	19,000
Transaction price	112,900	$ 112,900								$ 112,900
Development cost										80.00%
Increase (decrease) in transaction price											$ 52,200	$ 59,000
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 Development Compound
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount payable upon the effectiveness of the First Amendment	$ 5,000
Revenue recognized										$ 5,000
Janssen Biotech, Inc. | Second Generation Development Compound | Milestone payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount payable upon the effectiveness of the First Amendment										7,500
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
Development cost										20.00%
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. | First Amendment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
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
Increase (decrease) in transaction price										8,000
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]
Eligible payment receivable													$ 115,000
Janssen Biotech, Inc. | First Amendment | Second-Generation Phase 2b Milestone 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 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										14,600
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