License and Collaboration Agreements - Narrative (Details) - USD ($)			1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 03, 2020	Jan. 07, 2018	Oct. 31, 2014	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement				$ 79,853,000	$ 47,362,000	$ 216,644,000	$ 119,925,000
BeiGene Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Up-front fee received		$ 10,000,000.0
Revenue from performance obligation expected to be earned		$ 123,000,000.0
Termination of contract, period after first commercial sale of product		10 years
Period required for notice of termination of contract		60 days
Revenue from performance obligations satisfied during reporting period						29,000
BeiGene Agreement | Licenses of Intellectual Property
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned				0	0	0	0	$ 9,500,000
BeiGene Agreement | Manufacturing Supply Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation earned							2,600,000	$ 500,000
Payments received in advance				0	(1,000,000.0)	(300,000)	(2,800,000)
Revenue from performance obligations satisfied during reporting period							200,000
BeiGene Agreement | Milestone Payments
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue from performance obligation expected to be earned				5,000,000.0		5,000,000.0
Milestone payments earned				0	0	0	0
BeiGene Agreement | Royalties
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Revenue				0	0	0	0
Pfizer Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Termination of contract, period after first commercial sale of product			10 years
Period required for notice of termination of contract			60 days
Expenses related to collaboration agreement				$ 300,000	$ 1,500,000	4,800,000	5,500,000
Pfizer Agreement | Milestone Payments
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement							1,000,000.0
Pfizer Agreement | Research and Development Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Expenses related to collaboration agreement						$ 1,500,000	$ 4,500,000
ORIC Pharmaceuticals Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock received as part of stock issuance and license agreements (shares)	588,235
License agreement, period of transfer restrictions	18 months
License agreement, period of agreement after first commercial sale	10 years
ORIC Pharmaceuticals Agreement | Level 3
Research and Development Arrangement, Contract to Perform for Others [Line Items]
License agreement, transaction price	$ 11,400,000