Preferred Stock, Common Stock and Stockholders' Equity - Summary of Warrants Activity (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Warrants And Rights Note Disclosure [Abstract]
Warrants, Outstanding beginning balance	3,323,876
Warrants, Exercised	(526,315)
Warrants, Outstanding ending balance	2,797,561	3,323,876
Weighted Average Exercise Price, Outstanding beginning balance	$ 3.29
Weighted Average Exercise Price, Exercised	2.41
Weighted Average Exercise Price, Outstanding ending balance	$ 3.46	$ 3.29
Weighted Average Remaining Contractual Term (Years), Outstanding	3 years 11 months 8 days	4 years 11 months 15 days
Weighted Average Remaining Contractual Term (Years), Exercised	4 years 25 days