Stockholders' Equity - Summary of the Company's Stock Option Activity under Equity Incentive Plans (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) $ / shares shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options Available for Grant, Beginning Balance	2,695
Options Available for Grant, Options granted	(2,223)
Options Available for Grant, Options forfeited	115
Options Available for Grant, Ending Balance	587
Options Outstanding, Beginning Balance	2,031
Options Outstanding, Options granted	2,223
Options Outstanding, Options forfeited	(115)
Options Outstanding, Ending Balance	4,139
Options Outstanding, Vested and exercisable	864
Options Outstanding, Vested and expected to vest, Ending Balance	2,973
Options Outstanding, Unvested	3,275
Weighted Average Exercise Price, Beginning Balance | $ / shares	$ 2.01
Weighted Average Exercise Price, Options granted | $ / shares	0.72
Weighted Average Exercise Price, Options forfeited | $ / shares	3.27
Weighted Average Exercise Price, Ending Balance | $ / shares	1.53
Weighted Average Exercise Price, Vested and exercisable | $ / shares	2.40
Weighted Average Exercise Price, Vested and expected to vest, Ending Balance | $ / shares	1.41
Weighted Average Exercise Price, Unvested | $ / shares	$ 1.30
Weighted Average Remaining Contractual Life, Beginning Balance	8 years 5 months 9 days
Weighted Average Remaining Contractual Life, Ending Balance	8 years 6 months 18 days
Weighted Average Remaining Contractual Life, Vested and exercisable	6 years 9 months 15 days
Weighted Average Remaining Contractual Life, Vested and expected to vest, Ending Balance	8 years 3 months 18 days
Aggregate Intrinsic Value | $	$ 14
Aggregate Intrinsic Value, Vested and exercisable | $	0
Aggregate Intrinsic Value, Vested and expected to vest, Ending Balance | $	$ 11