Stockholders' Equity - Summary of Stock Option and Restricted Stock Unit Transactions (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Options [Member]
Shares Available for Grant
Options Available, Beginning balance	909,200	1,571,212
Options Available, Additional shares authorized	223,742	223,742
Options Available, Granted	(658,285)	(756,086)
Options Available, Exercised	0	0
Options Available, Canceled/Forfeited	202,321	115,920
Options Available, Ending balance	615,760	909,200	1,571,212
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance	1,667,153	1,026,987
Options granted	658,285	756,086
Options exercised	0	0
Options canceled/forfeited	(202,321)	(115,920)
Ending balance	2,123,117	1,667,153	1,026,987
Options vested at end of period (shares)	1,153,457
Options vested and expected to vest at end of period (shares)	2,123,117
Weighted-Average Exercise Price per Share
Beginning balance (in dollars per share)	$ 6.03	$ 9.99
Options granted (in dollars per share)	1.77	1.68
Options exercised (in dollars per share)	0	0
Options canceled/forfeited (in dollars per share)	6.99	12.72
Ending balance (in dollars per share)	4.62	$ 6.03	$ 9.99
Options vested at end of period (in dollars per share)	6.91
Options vested and expected to vest at end of period (in dollars per share)	$ 4.62
Weighted Average Remaining Contractual Term
Options outstanding at end of period	7 years 10 months 13 days	8 years 3 months 7 days	7 years 11 months 8 days
Options vested at end of period	7 years 2 months 26 days
Options vested and expected to vest at end of period	7 years 10 months 13 days
Restricted Stock Units [Member]
Shares Available for Grant
Options Available, Shares allocated to grants of restricted stock units	(61,218)	(245,588)