Schedule of Revenue from Collaborations and Services (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	$ 14,595	$ 4,469	$ 47,045	$ 11,827
Research Agreement | United Therapeutics Corporation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	200		5,900
Collaboration and License Agreement | United Therapeutics Corporation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	7,900		23,300
Collaborations and services
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	8,193	82	29,502	232
Collaborations and services | License Agreement | United Therapeutics Corporation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	7,861		23,255
Collaborations and services | Research Agreement | United Therapeutics Corporation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	158		5,874
Collaborations and services | Collaboration and License Agreement | Receptor
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	62	45	187	171
Collaborations and services | Supply and Distribution Agreement | Biomm
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	75		75
Collaborations and services | License and Distribution Agreement | Cipla Ltd
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	$ 37	$ 37	$ 111	$ 61