Subsequent Events - Additional Information (Details) - USD ($)		1 Months Ended				9 Months Ended
	Nov. 03, 2020	Dec. 31, 2020	Nov. 30, 2020	Oct. 31, 2020	May 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Shares issued						48,958,829	33,645,447
Gross proceeds from issuance of preferred stock						$ 106,631,000
Convertible preferred stock converted into shares						48,958,829
Common stock, shares authorized						80,529,575	53,070,161
Roche License Agreement | Scenario Forecast
Subsequent Event [Line Items]
Financial advisor fee paid		$ 7,000,000
Subsequent Event
Subsequent Event [Line Items]
Common stock, shares authorized			300,000,000
Subsequent Event | 2020 Incentive Award Plan
Subsequent Event [Line Items]
Common stock, shares authorized				7,924,000
Stock option plan, effective date				Oct. 29, 2020
Subsequent Event | 2020 Employee Stock Purchase Plan
Subsequent Event [Line Items]
Common stock, shares authorized				1,187,000
Stock option plan, effective date				Oct. 29, 2020
Subsequent Event | IPO
Subsequent Event [Line Items]
Share price	$ 24.00		$ 24.00
Aggregated gross proceeds from initial public offering ("IPO")	$ 345,000,000		$ 345,000,000
Underwriting discounts and commissions	24,150,000		24,150,000
Offering expenses	$ 3,200,000		$ 3,200,000
Subsequent Event | Common Stock | IPO
Subsequent Event [Line Items]
Shares issued	14,375,000		14,375,000
Subsequent Event | Undesignated Preferred Stock
Subsequent Event [Line Items]
Preferred stock, shares authorized			10,000,000
Subsequent Event | Roche License Agreement
Subsequent Event [Line Items]
Upfront payment received			$ 350,000,000
Maximum | Subsequent Event | Over-Allotment Option
Subsequent Event [Line Items]
Shares issued	1,875,000		1,875,000
Maximum | Subsequent Event | Roche License Agreement | Development and Regulatory
Subsequent Event [Line Items]
Milestones receivable upon achievement aggregate				$ 330,000,000
Maximum | Subsequent Event | Roche License Agreement | Sales Based
Subsequent Event [Line Items]
Milestones receivable upon achievement aggregate				$ 320,000,000
Series D-1 Preferred Stock
Subsequent Event [Line Items]
Right to purchase price, per share					$ 11.98
Series D-1 Preferred Stock | Subsequent Event
Subsequent Event [Line Items]
Shares issued				8,973,261
Share price				$ 11.98
Gross proceeds from issuance of preferred stock				$ 107,500,000
Series D-1 Preferred Stock | Maximum
Subsequent Event [Line Items]
Options to purchase shares					8,973,261
Series A, B, C, D and D-1 Convertible Preferred Stock | Subsequent Event | Common Stock | IPO
Subsequent Event [Line Items]
Convertible preferred stock converted into shares	57,932,090		57,932,090