Stock Plan and Stock-Based Compensation - Assumptions used to Calculate Fair Value of Stock-Based Compensation (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)	10 years
Dividend yield	0.00%
Employee Stock Option
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Risk-free interest rate, minimum	1.60%	1.20%
Risk-free interest rate, maximum	2.30%	3.10%
Expected term (in years)	6 years 7 days
Volatility, minimum	71.80%	58.70%
Volatility, maximum	74.60%	75.50%
Dividend yield	0.00%	0.00%
Employee stock purchase plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Risk-free interest rate, minimum	1.60%	2.10%
Risk-free interest rate, maximum	2.30%	2.60%
Volatility, minimum	64.80%	54.30%
Volatility, maximum	77.10%	65.50%
Dividend yield	0.00%	0.00%
Minimum | Employee Stock Option
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)		5 years 1 month 28 days
Minimum | Employee stock purchase plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)	6 months	6 months
Maximum | Employee Stock Option
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)		9 years 11 months 12 days
Maximum | Employee stock purchase plan
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)	2 years	2 years