Warrants (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Class of Warrant or Right [Line Items]
Weighted average remaining contractual life	5 years
Warrant Exercise Price Range One 4.00 - 5.00
Class of Warrant or Right [Line Items]
Warrants outstanding	116,875
Weighted average remaining contractual life	2 months 26 days
Warrants exercisable	116,875
Weighted average exercise price per share | $ / shares	$ 4.41
Warrant Exercise Price Range Two 9.00 - 10.00
Class of Warrant or Right [Line Items]
Warrants outstanding	2,681,666
Weighted average remaining contractual life	3 years 6 months 4 days
Warrants exercisable	2,681,666
Weighted average exercise price per share | $ / shares	$ 9.58
Warrant Exercise Price Range Three 11.00
Class of Warrant or Right [Line Items]
Warrants outstanding	850,000
Weighted average remaining contractual life	4 years 11 months 8 days
Warrants exercisable	850,000
Weighted average exercise price per share | $ / shares	$ 11.00
Warrant Exercise Price Range Four 4.50 - 10.00
Class of Warrant or Right [Line Items]
Warrants outstanding	3,648,541
Weighted average remaining contractual life	3 years 8 months 26 days
Warrants exercisable	3,648,541
Weighted average exercise price per share | $ / shares	$ 9.75