Stock-Based Compensation Expense - Summary of Stock Option Activity Under Plans (Details) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding December 31, 2019 | shares	792,439
Shares, Granted | shares	702,505
Shares, Exercised | shares	(254)
Shares, Cancelled | shares	(119,383)
Shares, Outstanding at September 30, 2020 | shares	1,375,307	792,439
Shares, Exercisable at September 30, 2020 | shares	571,355
Shares, Vested and expected to vest at September 30, 2020 | shares	1,375,307
Weighted Average Exercise Price, Outstanding December 31, 2019 | $ / shares	$ 6.59
Weighted Average Exercise Price, Granted | $ / shares	14.42
Weighted Average Exercise Price, Exercised | $ / shares	1.73
Weighted Average Exercise Price, Cancelled | $ / shares	9.41
Weighted Average Exercise Price, Outstanding at September 30, 2020 | $ / shares	10.34	$ 6.59
Weighted Average Exercise Price, Exercisable at September 30, 2020 | $ / shares	9.20
Weighted Average Exercise Price, Vested and expected to vest at September 30, 2020 | $ / shares	$ 10.34
Outstanding, Weighted Average Remaining Contractual Life (in years)	7 years 9 months 18 days	7 years 3 months 18 days
Exercisable, Weighted Average Remaining Contractual Life (in years)	5 years 10 months 24 days
Vested and expected to vest, Weighted Average Remaining Contractual Life (in years)	7 years 9 months 18 days
Aggregate Intrinsic Value, Outstanding December 31, 2019 | $	$ 5,031	$ 3,363
Aggregate Intrinsic Value, Exercisable at September 30, 2020 | $	2,813
Aggregate Intrinsic Value, Vested and expected to vest at September 30, 2020 | $	$ 5,031