License and Collaboration Agreements - Summary of Revenues by Collaboration and by Category of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	$ 64,530	$ 1,750	$ 68,030	$ 5,250
Gilead License To Zimberelimab [Member]
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	55,096		55,096
Gilead Access Rights [Member]
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	7,684		7,684
Taiho Collaboration Agreement
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	$ 1,750	$ 1,750	$ 5,250	$ 5,250