Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Schedule of Fair Value of ESPP Shares Using Option Pricing Model (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, Minimum	80.90%	73.20%	72.70%
Expected volatility, Maximum	84.90%	87.40%	74.90%
Risk-free interest rate, Minimum	0.60%	0.20%	1.40%
Risk-free interest rate, Maximum	1.30%	1.60%	2.60%
Expected dividend	0.00%
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	6 months
Expected volatility, Minimum	65.90%	63.00%	63.00%
Expected volatility, Maximum	111.40%	111.40%	83.20%
Risk-free interest rate	0.10%
Risk-free interest rate, Minimum		0.10%	1.90%
Risk-free interest rate, Maximum		1.90%	2.50%