Stock-Based Compensation - Summary of Activity Under Stock Incentive Plans (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Subject to Outstanding, Beginning Balance	4,578,782
Shares Subject to Outstanding, Options granted	0	0
Shares Subject to Outstanding, Options cancelled and forfeited	(198,483)
Shares Subject to Outstanding, Ending Balance	4,380,299
Shares Subject to Outstanding, Vested and expected to vest	4,346,958
Shares Subject to Outstanding, Exercisable	2,713,195
Weighted-Average Exercise Price Per Share, Outstanding Beginning Balance	$ 4.38
Weighted-Average Exercise Price Per Share, Options cancelled and forfeited	3.36
Weighted Average Exercise Price Per Share, Outstanding Ending Balance	4.42
Weighted Average Exercise Price Per Share, Vested and expected to vest	4.41
Weighted Average Exercise Price Per Share, Exercisable	$ 3.65