Stockholders' Equity - Schedule of Shares of Common Stock Reserved for Issuance (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Total	32,191,275	31,116,719
Reserve balance for Sales Agreement
Class of Stock [Line Items]
Total	14,182,900	14,190,300
Common stock options outstanding
Class of Stock [Line Items]
Total	10,660,410	10,017,918
Common stock options available for grant
Class of Stock [Line Items]
Total	6,739,933	6,186,497
ESPP shares available for purchase
Class of Stock [Line Items]
Total	590,219	700,074
401(k) Matching Plan
Class of Stock [Line Items]
Total	17,813	21,930