Stock-Based Compensation - Schedule of Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Stock Options Activity [Abstract]
Number of Shares, Outstanding, Beginning balance	5,423,741
Number of Shares, Granted	4,407,758
Number of Shares, Forfeited	(434,025)
Number of Shares, Cancelled	(467,985)
Number of Shares, Exercised	(628,670)
Number of Shares, Outstanding, Ending balance	8,300,819	5,423,741
Weighted Average Exercise Price, Outstanding	$ 2.82
Weighted Average Exercise Price, Granted	2.76
Weighted Average Exercise Price, Forfeited	4.70
Weighted Average Exercise Price, Cancelled	6.80
Weighted Average Exercise Price, Exercised	0.41
Weighted Average Exercise Price, Outstanding	$ 2.63	$ 2.82
Weighted-Average Remaining Contractual Term (Years)	8 years 2 months 23 days	7 years 11 months 12 days