Stockholders' Equity and Stock-Based Compensation - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Outstanding, Options granted			567,123
Stock-based compensation expense	$ 2,718,000	$ 1,166,000	$ 4,645,000	$ 2,130,000
Stock repurchase right	339,102		339,102		524,513
Accrued repurchase liability for common stock early exercises	$ 164,000		$ 164,000		$ 238,000
2016 Plan and Amended and Restated 2018 Stock Option and Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation cost related to unvested stock	$ 25,700,000		$ 25,700,000
Unrecognized stock-based compensation cost, to be recognized weighted-average period			2 years 11 months 23 days
Non Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Outstanding, Options granted	17,130	0	17,595	18,500
Stock-based compensation expense	$ 200,000	$ 100,000	$ 400,000	$ 100,000