Summary of Warrant (Detail) - Warrant [Member] - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
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Number of warrants, Outstanding	3,648,541
Number of Warrants granted	0
Number of Warrants exercised	(268,663)
Number of Warrants expired/forfeited	(11,250)
Number of warrants, Outstanding	3,368,628	3,648,541
Weighted Average Exercise Price
Warrants outstanding Balance	$ 9.75
Warrants granted	0
Warrants exercised	7.82
Warrants expired/forfeited	0
Warrants outstanding Balance	$ 9.92	$ 9.75
Weighted Average Remaining Contractual Term (Years)
Warrants granted	0 months
Warrants exercised	0 months
Warrants expired/forfeited	0 months
Warrants outstanding Balance	3 years 2 months 16 days	3 years 8 months 26 days
Aggregate Intrinsic Value
Warrants outstanding Balance	$ 14.25
Warrants granted	0
Warrants exercised	10.58
Warrants expired/forfeited	0
Warrants outstanding Balance	$ 12.15	$ 14.25