Stock-Based Compensation Expense - Common stock reserved for future issuance (Details) - shares	Mar. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	7,475,130	6,878,511
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	757,694	484,027
Stock options issued and outstanding under the 2006, 2015 and 2021 plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	6,150,402	5,754,005
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	567,034	640,479