Common Stock and Stock-Based Awards - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Number of Shares, Beginning Balance	8,310,683
Number of Shares, Granted	2,957,750
Number of Shares, Exercised	(110,967)
Number of Shares, Forfeited	(401,873)
Number of Shares, Ending Balance	10,755,593	8,310,683
Number of Shares, Options vested and expected to vest	10,755,593
Number of Shares, Options exercisable	5,080,248
Weighted Average Exercise Price, Beginning Balance	$ 10.36
Weighted Average Exercise Price, Granted	3.30
Weighted Average Exercise Price, Exercised	0.48
Weighted Average Exercise Price, Forfeited	8.62
Weighted Average Exercise Price, Ending Balance	8.58	$ 10.36
Weighted Average Exercise Price, Options vested and expected to vest	8.58
Weighted Average Exercise Price, Options exercisable	$ 12.41
Weighted Average Remaining Contractual Term, Outstanding	7 years 4 months 17 days	7 years 3 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	7 years 4 months 17 days
Weighted Average Remaining Contractual Term, Options exercisable	5 years 4 months 17 days
Aggregate Intrinsic Value, Outstanding	$ 4,055	$ 3,427
Aggregate Intrinsic Value, Options vested and expected to vest	4,055
Aggregate Intrinsic Value, Options exercisable	$ 3,110