Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Number of Shares
Outstanding at December 31, 2019	4,364,839
Granted	1,663,000
Forfeited	(1,862,404)
Outstanding at September 30, 2020	4,165,435	4,364,839
Exercisable at September 30, 2020	2,776,235
Vested and expected to vest at September 30, 2020	4,082,185
Weighted Average Exercise Price Per Share
Outstanding at December 31, 2019	$ 5.30
Granted	1.56
Forfeited	3.52
Outstanding at September 30, 2020	4.60	$ 5.30
Exercisable at September 30, 2020	5.58
Vested and expected to vest at September 30, 2020	$ 4.65
Weighted Average Remaining Contractual Term, Outstanding	6 years 10 months 24 days	7 years 3 months 25 days
Weighted Average Remaining Contractual Term, Exercisable at March 31, 2020	6 years 2 months 8 days
Weighted Average Remaining Contractual Term, Vested and expected to vest at March 31, 2020	7 years 10 days
Aggregate Intrinsic Value, Outstanding	$ 7	$ 132
Aggregate Intrinsic Value, Exercisable at March 31, 2020	7
Aggregate Intrinsic Value, Vested and expected to vest at March 31, 2020	$ 7