Research, Collaboration and Licensing Agreements - Schedule Of Collaborative Arrangements and Noncollaborative Arrangement Transactions (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Mar. 31, 2020	Jan. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue			$ 8,269	$ 11,925
Bei Gene | Milestone revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	$ 5,000		5,000	0
Bei Gene | Drug supply revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue			2,159	0
Bei Gene | Recognition of upfront fee
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue			0	3,530
Eli Lilly and Company | Milestone revenue
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue		$ 8,000	0	8,000
Other | Research support and other payments
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue			$ 1,110	$ 395