Stock-Based Compensation - Schedule of Stock Option Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation Stock Options Activity [Abstract]
Number of Shares, Outstanding, Beginning balance	8,300,819
Number of Shares, Granted	5,368,755
Number of Shares, Forfeited	(797,301)
Number of Shares, Cancelled	(152,946)
Number of Shares, Exercised	(230,776)
Number of Shares, Outstanding, Ending balance	12,488,551	8,300,819
Weighted Average Exercise Price, Outstanding	$ 2.63
Weighted Average Exercise Price, Granted	2.81
Weighted Average Exercise Price, Forfeited	3.53
Weighted Average Exercise Price, Cancelled	4.61
Weighted Average Exercise Price, Exercised	0.71
Weighted Average Exercise Price, Outstanding	$ 2.66	$ 2.63
Weighted-Average Remaining Contractual Term (Years)	8 years 29 days	8 years 2 months 23 days