Stockholders' Equity - Summary of the Company's Stock Option Activity under 2015 and 2005 Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options Available for Grant, Beginning Balance	2,695,000	54,000
Options Available for Grant, Options granted	(2,569,000)	(1,842,000)
Options Available for Grant, Options forfeited	423,000	483,000
Options Available for Grant, Options authorized		4,000,000
Options Available for Grant, Ending Balance	549,000	2,695,000
Options Outstanding, Beginning Balance	2,031,000	672,000
Options Outstanding, Options granted	2,569,000	1,842,000
Options Outstanding, Options forfeited	(423,000)	(483,000)
Options Outstanding, Ending Balance	4,177,000	2,031,000
Weighted Average Exercise Price, Beginning Balance	$ 2.01	$ 3.63
Options Outstanding, Vested and exercisable	1,053,000
Weighted Average Exercise Price, Options granted	$ 0.70	1.95
Options Outstanding, Vested and expected to vest, Ending Balance	3,226,000
Weighted Average Exercise Price, Options forfeited	$ 1.74	1.93
Options Outstanding, Unvested	3,124,000
Weighted Average Exercise Price, Ending Balance	$ 1.47	$ 2.01
Weighted Average Exercise Price, Vested and exercisable	2.20
Weighted Average Exercise Price, Vested and expected to vest, Ending Balance	1.33
Weighted Average Exercise Price, Unvested	$ 1.23
Weighted Average Remaining Contractual Life, Beginning Balance	8 years 5 months 27 days
Weighted Average Remaining Contractual Life, Ending Balance	8 years 5 months 9 days
Weighted Average Remaining Contractual Life, Ending Balance	8 years 1 month 21 days
Weighted Average Remaining Contractual Life, Vested and exercisable	6 years 11 months 16 days
Weighted Average Remaining Contractual Life, Vested and expected to vest, Ending Balance	8 years
Aggregate Intrinsic Value	$ 0
Aggregate Intrinsic Value, Vested and exercisable	0
Aggregate Intrinsic Value, Vested and expected to vest, Ending Balance	$ 0