Common Stock Warrant Activity (Detail) - Warrant	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Shares
Outstanding, December 31, 2017 | shares	13,229,778
Granted | shares	290
Exercised | shares	(2,533,042)
Forfeited/cancelled | shares	0
Outstanding, September 30, 2018 | shares	10,697,026
Weighted Average Exercise Price
Outstanding, December 31, 2017 | $ / shares	$ 3.35
Granted | $ / shares	5.15
Exercised | $ / shares	2.50
Forfeited/cancelled | $ / shares	0
Outstanding, September 30, 2018 | $ / shares	$ 3.54