- Summary of Stock Option Transactions (Detail) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Shares Available for Grant
Options Available, Amendment to plan to authorize additional shares	8,929,188
Stock Options [Member]
Shares Available for Grant
Options Available, Beginning balance	958,856
Options Available, Additional shares authorized	671,478
Options Available, Granted	(60,000)
Options Available, Exercised	0
Options Available, Canceled/Forfeited	33,583
Options Available, Ending balance	10,533,105	958,856
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance	2,908,430
Options granted	60,000
Options canceled/forfeited	(33,583)
Ending balance	2,934,847	2,908,430
Weighted-Average Exercise Price per Share
Beginning balance (in dollars per share)	$ 3.42
Options granted (in dollars per share)	0.65
Options canceled/forfeited (in dollars per share)	4.46
Ending balance (in dollars per share)	$ 3.35	$ 3.42
Weighted Average Remaining Contractual Term
Options outstanding at end of period	8 years 3 months 11 days	8 years 5 months 23 days
Options vested at end of period	7 years 11 months 23 days
Options vested and expected to vest at end of period	8 years 3 months 11 days
Options vested at end of period (shares)	1,593,754
Options vested at end of period (in dollars per share)	$ 3.98
Options vested and expected to vest at end of period (shares)	2,934,847
Options vested and expected to vest at end of period (in dollars per share)	$ 3.35