Common Stock - Schedule of Shares Reserved for Future Issuance (Details) - shares	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jan. 31, 2019	Jul. 31, 2018
Class Of Stock [Line Items]
Total shares reserved for future issuance	7,416,476		20,346,844
Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Total shares reserved for future issuance			18,442,233
Exercises of Outstanding Stock Option Awards
Class Of Stock [Line Items]
Total shares reserved for future issuance	2,808,477		1,337,501
Shares of Common Stock Available for Future Grants under the 2015 Equity Incentive Plan, as Amended
Class Of Stock [Line Items]
Total shares reserved for future issuance		1,400,000	567,110	400,000	1,000,000
Shares of Common Stock Available for Future Grants under the 2020 Equity Incentive Plan
Class Of Stock [Line Items]
Total shares reserved for future issuance	3,907,999
Shares of Common Stock Available for Future Issuance under the 2020 ESPP
Class Of Stock [Line Items]
Total shares reserved for future issuance	700,000