Stockholders' Equity - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stock Option
Number of Shares
Outstanding, beginning of year (in shares)	861,366	778,590
Granted (in shares)	2,146,190	379,000
Canceled (in shares)	(74,324)	(296,224)
Exercised (in shares)	0	0
Outstanding, end of year (in shares)	2,933,232	861,366
Exercisable at end of the year (in shares)	408,042	482,366
Weighted Average Exercise Price
Outstanding, beginning of year (in dollars per share)	$ 3.99	$ 5.36
Granted (in dollars per share)	3.85	2.30
Canceled (in dollars per share)	6.71	5.40
Exercised (in dollars per share)	0.00	0.00
Outstanding, end of year (in dollars per share)	3.82	3.99
Exercisable at end of the year (in dollars per share)	$ 5.07	$ 5.33
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Outstanding, Aggregate Intrinsic Value		$ 76
Exercisable, Aggregate Intrinsic Value		$ 0
Outstanding, Weighted Average Remaining Contractual Term		7 years 6 months
Exercisable, Weighted Average Remaining Contractual Life		1 year 5 months 9 days
Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Unvested options outstanding (in shares)	658,000