Stock Plans and Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - Employee And Non Employee - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 21,825	$ 8,981	$ 3,874
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	11,195	4,152	2,255
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 10,630	$ 4,829	$ 1,619