Summary of Warrant (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 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	(210,625)
Number of Warrants expired/forfeited	(11,250)
Number of warrants, Outstanding	3,426,666	3,648,541
Weighted Average Exercise Price
Warrants outstanding Balance	$ 9.75
Warrants granted	0
Warrants exercised	7.27
Warrants expired/forfeited	0
Warrants outstanding Balance	$ 9.91	$ 9.75
Weighted Average Remaining Contractual Term (Years)
Warrants outstanding Balance	3 years 5 months 16 days	3 years 8 months 26 days
Aggregate Intrinsic Value
Warrants outstanding Balance	$ 14.25
Warrants granted	0
Warrants exercised	10.46
Warrants expired/forfeited	0
Warrants outstanding Balance	$ 15.95	$ 14.25
Warrant [Member]
Weighted Average Remaining Contractual Term (Years)
Warrants granted	0 years
Warrants exercised	0 years
Warrants expired/forfeited	0 years