License and Collaboration Agreements - Summary of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
License And Collaboration Agreements [Line Items]
License revenue	$ 9,487	$ 64,530	$ 1,750	$ 1,750	$ 9,750	$ 1,750	$ 1,750	$ 1,750
Gilead and Taiho | License
License And Collaboration Agreements [Line Items]
License revenue									$ 55,096	$ 8,000	$ 3,000
Gilead and Taiho | Collaboration Revenue
License And Collaboration Agreements [Line Items]
License revenue									22,421	7,000	5,353
Gilead and Taiho | Collaboration and License
License And Collaboration Agreements [Line Items]
License revenue									$ 77,517	$ 15,000	$ 8,353