Stock-based Compensation - Summary of Stock Option Activity (Details) - 2015 Incentive Stock Option and Grant Plan $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options, Outstanding as of December 31, 2019 | shares	2,368,950
Number of options, Granted | shares	1,467,424
Number of options, Exercised | shares	(251,466)
Number of options, Cancelled or forfeited | shares	(1,229,054)
Number of options, Outstanding as of September 30, 2020 | shares	2,355,854	2,368,950
Number of options, Options exercisable | shares	365,732	733,310
Weighted-average exercise price, Outstanding as of December 31, 2019 | $ / shares	$ 4.35
Weighted-average exercise price, Granted | $ / shares	4.98
Weighted-average exercise price, Exercised | $ / shares	3.17
Weighted-average exercise price, Cancelled or forfeited | $ / shares	4.52
Weighted-average exercise price, Outstanding as of September 30, 2020 | $ / shares	4.82	$ 4.35
Weighted-average exercise price, Options exercisable | $ / shares	$ 4.04	$ 3.40
Weighted average remaining contractual term (in years), Options outstanding	8 years 10 months 20 days	8 years 1 month 9 days
Weighted average remaining contractual term (in years), Options exercisable	7 years 3 months 10 days	7 years 4 months 28 days
Aggregate intrinsic value, Outstanding as of December 31, 2019 | $	$ 10,309
Aggregate intrinsic value, Exercised | $	2,442
Aggregate intrinsic value, Outstanding as of September 30, 2020 | $	11,367	$ 10,309
Aggregate intrinsic value, Options exercisable | $	$ 6,949	$ 2,275