Commitments and Contingencies - Additional Information (Details) $ in Thousands					1 Months Ended				12 Months Ended
	Oct. 24, 2019 USD ($)	Aug. 03, 2018 USD ($)	Apr. 28, 2017 USD ($)	Aug. 03, 2015 USD ($)	Oct. 31, 2019 USD ($)	Jul. 31, 2019 USD ($)	Oct. 31, 2018 USD ($)	Mar. 31, 2016 USD ($) Installment	Dec. 31, 2020 USD ($) ft² Option	Dec. 31, 2019 USD ($)	Jan. 01, 2020 USD ($)	Oct. 25, 2019 USD ($)
Commitments And Contingencies [Line Items]
Operating leases, number of square feet | ft²									83,000
Operating leases remaining lease terms									108 months
Operating lease, option to extend, description									The manufacturing and laboratory and office space lease agreements include two options to extend the term for a period of 5 years each.
Operating lease, option to extend									true
Operating lease, extended term									5 years
Operating lease, number of options to extend term | Option									2
Operating lease, commencement date					Jul. 29, 2020	Jun. 26, 2020	Apr. 01, 2019	Jun. 30, 2016
Operating lease, initial term								10 years 6 months
Security deposit					$ 300	$ 100		$ 100
Operating lease, termination date								Apr. 30, 2019
Operating lease, termination fee								$ 1,500
Operating lease, termination fee, number of installments | Installment								3
Operating lease, termination fee, term								1 year 6 months
Operating lease, expiration date					Dec. 31, 2029	Dec. 31, 2029	Dec. 31, 2029
Tenant improvements						$ 2,900	$ 4,200
Additional tenant reimbursements					$ 1,500
Operating lease right-of-use assets									$ 24,986
Initial lease liability									30,182
Accumulated deficit									281,885	$ 152,221
Operating lease expense									6,000	$ 2,500
Operating lease, payments									$ 4,800
Operating lease, weighted-average remaining lease term									8 years 8 months 12 days
Operating lease, weighted-average discount rate									8.90%
License Agreement | Janssen Biotech Inc.
Commitments And Contingencies [Line Items]
Upfront fee				$ 200
Milestone payments									$ 4,000
Initial milestone payments payable									75,800
Additional milestone payments payable									$ 46,800
License Agreement | Genus Oncology, LLC
Commitments And Contingencies [Line Items]
Upfront fee	$ 1,500
Initial milestone payments payable												$ 71,000
Additional fee payable to exercise option	$ 1,500
Commercial License Agreement | TeneoBio, Inc.
Commitments And Contingencies [Line Items]
Upfront fee		$ 4,000	$ 500
Initial milestone payments payable			20,500
Additional milestone payments payable			$ 20,500
Milestone payments payable		$ 31,000
ASC 842
Commitments And Contingencies [Line Items]
Operating lease, option to extend, description									The leases in San Diego include an option to extend, which was not recognized as part of the lease liability and ROU lease assets as the Company was not reasonably certain it would exercise the extension right.
Operating lease, option to extend									true
Initial lease receivables											$ 2,700
Operating lease right-of-use assets											22,300
Deferred rent balance											2,300
Initial lease liability											27,300
ASC 842 | Cumulative Adjustment
Commitments And Contingencies [Line Items]
Accumulated deficit											100
Other Current Assets
Commitments And Contingencies [Line Items]
Receivable for amounts to be reimbursed									$ 100
Property and Equipment
Commitments And Contingencies [Line Items]
Tenant improvements									$ 13,300
Property and Equipment | ASC 842 | Adoption of ASC 842 Adjustment
Commitments And Contingencies [Line Items]
Derecognition of construction in progress related to manufacturing facility											2,100
Other Long-Term Liabilities | ASC 842 | Adoption of ASC 842 Adjustment
Commitments And Contingencies [Line Items]
Derecognition of construction financing obligation related to manufacturing facility											2,500
Prepaid and Other Current Assets | ASC 842 | Adoption of ASC 842 Adjustment
Commitments And Contingencies [Line Items]
Derecognition of other receivables related to manufacturing facility											$ 300
Maximum
Commitments And Contingencies [Line Items]
Operating lease remaining lease term dedicated to manufacturing suites									12 months