Stockholders' Equity - Summary of Stock Option Transactions (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options granted	0
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance	1,026,987
Options granted	616,500	12,000
Options exercised	0
Options canceled/forfeited	(92,177)
Ending balance	1,551,310
Weighted-Average Exercise Price per Share
Beginning balance (in dollars per share)	$ 9.99
Options granted (in dollars per share)	1.60
Options exercised (in dollars per share)	0
Options canceled/forfeited (in dollars per share)	14.54
Ending balance (in dollars per share)	$ 6.38
Weighted Average Remaining Contractual Term
Options outstanding at end of period	8 years 10 months 21 days
Options vested at end of period	7 years 9 months 29 days
Options vested and expected to vest at end of period	8 years 10 months 21 days
Options vested at end of period (shares)	509,830
Options vested at end of period (in dollars per share)	$ 13.15
Options vested and expected to vest at end of period (shares)	1,551,310
Options vested and expected to vest at end of period (in dollars per share)	$ 6.38