Stockholders' Equity Common Stock - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Number of Shares, Beginning Balance	7,561,719
Number of Shares, Granted	2,456,850
Number of Shares, Exercised	(90,125)
Number of Shares, Forfeited	(1,617,761)
Number of Shares, Ending Balance	8,310,683	7,561,719
Number of Shares, Options vested and expected to vest	8,310,683
Number of Shares, Options exercisable	4,815,001
Weighted Average Exercise Price, Beginning Balance	$ 12.26
Weighted Average Exercise Price, Granted	5.79
Weighted Average Exercise Price, Exercised	1.61
Weighted Average Exercise Price, Forfeited	12.82
Weighted Average Exercise Price, Ending Balance	10.36	$ 12.26
Weighted Average Exercise Price, Options vested and expected to vest	10.36
Weighted Average Exercise Price, Options exercisable	$ 12.47
Weighted Average Remaining Contractual Term, Outstanding	7 years 3 days	7 years 2 months 23 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	7 years 3 days
Weighted Average Remaining Contractual Term, Options exercisable	5 years 9 months 10 days
Aggregate Intrinsic Value, Outstanding	$ 3,427	$ 4,958
Aggregate Intrinsic Value, Options vested and expected to vest	3,427
Aggregate Intrinsic Value, Options exercisable	$ 3,296