Stockholders' Equity - Summary of the Company's Stock Option Activity under Equity Incentive Plans (Detail) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) $ / shares shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options Available for Grant, Beginning Balance	549,000
Options Available for Grant, Options authorized	2,000,000
Options Available for Grant, Options granted	(2,120,000)
Options Available for Grant, Options forfeited	361,000
Options Available for Grant, Ending Balance	790,000
Options Outstanding, Beginning Balance	4,177,000
Options Outstanding, Options granted	2,120,000
Options Outstanding, Options forfeited	(361,000)
Options Outstanding, Ending Balance	5,936,000
Options Outstanding, Vested and exercisable	1,557,000
Options Outstanding, Vested and expected to vest, Ending Balance	4,394,000
Options Outstanding, Unvested	4,379,000
Weighted Average Exercise Price, Beginning Balance | $ / shares	$ 1.47
Weighted Average Exercise Price, Options granted | $ / shares	0.40
Weighted Average Exercise Price, Options forfeited | $ / shares	1.19
Weighted Average Exercise Price, Ending Balance | $ / shares	1.11
Weighted Average Exercise Price, Vested and exercisable | $ / shares	1.68
Weighted Average Exercise Price, Vested and expected to vest, Ending Balance | $ / shares	1.04
Weighted Average Exercise Price, Unvested | $ / shares	$ 0.91
Weighted Average Remaining Contractual Life, Beginning Balance	8 years 1 month 21 days
Weighted Average Remaining Contractual Life, Ending Balance	8 years 7 months 2 days
Weighted Average Remaining Contractual Life, Vested and exercisable	7 years 7 months 21 days
Weighted Average Remaining Contractual Life, Vested and expected to vest, Ending Balance	8 years 4 months 28 days
Aggregate Intrinsic Value | $	$ 933
Aggregate Intrinsic Value, Vested and exercisable | $	55
Aggregate Intrinsic Value, Vested and expected to vest, Ending Balance | $	$ 600