Stock-Based Compensation - Summary of Stock Option Activity (Details) - 2002 Plan and 2018 Plan - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total Options
Outstanding, beginning balance (in shares)	2,577,718	1,545,403
Granted (in shares)	1,227,159	1,260,540
Exercised (in shares)	(51,572)	(143,654)
Cancelled or expired (in shares)	(155,145)	(84,571)
Outstanding, ending balance (in shares)	3,598,160	2,577,718	1,545,403
Vested and expected to vest (in shares)	3,598,160
Vested and exercisable (in shares)	1,864,186
Weighted- Average Exercise Price Per Share
Outstanding, beginning balance (in usd per share)	$ 3.29	$ 2.48
Granted (in usd per share)	5.09	4.19
Exercised (in usd per share)	1.85	1.71
Cancelled or expired (in usd per share)	4.89	4.65
Outstanding, ending balance (in usd per share)	3.85	$ 3.29	$ 2.48
Vested and expected to vest (in usd per share)	3.85
Vested and exercisable (in usd per share)	$ 3.26
Weighted- Average Remaining Contractual Term (in years)
Outstanding (in years)	7 years 6 months	7 years 10 months 24 days	7 years 7 months 6 days
Vested and expected to vest (in years)	7 years 6 months
Vested and exercisable (in years)	6 years 6 months
Aggregate Intrinsic Value
Outstanding	$ 1,737,432	$ 7,914,459	$ 1,593,487
Vested and expected to vest	1,737,432
Vested and exercisable	$ 1,559,887