Collaborations and License Agreements - Additional Information (Detail)	1 Months Ended		3 Months Ended		12 Months Ended
	Oct. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2021 USD ($) ft²	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Acquired in-process research and development					$ 70,000,000	$ 0	$ 0
Transaction costs					8,638,000	0	14,573,000
Revenues					54,000	319,000	806,431,000
Royalty revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues					0	262,000	$ (853,000)
United Therapeutics
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative agreement upfront payments				$ 800,000,000
Collaboration agreement estimated transaction price				800,000,000
United Therapeutics | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement				400,000,000
United Therapeutics | Non U.S. Market
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement				150,000,000
United Therapeutics | U.S. Market
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement				$ 250,000,000
Aristea Therapeutics, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement, rights and obligations, contractual upfront payments					60,000,000
Acquired in-process research and development					70,000,000
Aristea Therapeutics, Inc. | Series B Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement, rights and obligations, contractual upfront payments					10,000,000
United Therapeutics
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement right description							In November 2018, the Company entered into an exclusive license agreement with United Therapeutics. Under this agreement, the Company granted United Therapeutics an exclusive, worldwide, royalty-bearing license to develop, manufacture and commercialize ralinepag in any formulation. This transaction was completed in January 2019.
Collaborative agreement completion period							2019-01
Transaction costs					17,000,000		$ 14,600,000
Everest
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognized revenues					$ 0	0	5,000,000
Everest | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement								$ 110,000,000
Eisai | Eisai Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Defective manufacturing loss percentage					50.00%
Eisai | Eisai Agreement | Royalty revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues						300,000	(1,100,000)
Boehringer Ingelheim
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement					$ 246,000,000
Revenues					0	$ 0	1,700,000
Recognized milestone revenue	$ 1,500,000	$ 3,500,000
Boehringer Ingelheim | Beacon Discovery, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payable on milestone achievements					$ 7,000,000
Outpost Medicine
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognized revenues							$ 500,000
Beacon
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from collaborative arrangement, due to business acquisition			$ 1,100,000
Collaborative arrangement, contingent consideration, performance metric achievement period					4 years
Collaborative arrangement, contingent consideration, revenue receivable upon achievement of performance metrics					$ 2,000,000
Beacon | Beacon Discovery, Inc. | Sublease Agreement | Variable Interest Entity, Primary Beneficiary
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Area of office space | ft²					30,000