Quarterly report pursuant to Section 13 or 15(d)

Summary of Warrant (Detail)

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Summary of Warrant (Detail) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Shares [Abstract]    
Number of warrants, Outstanding 3,648,541  
Number Of Warrants Granted 0  
Number Of Warrants Exercised (191,625)  
Class Of Warrant Or Right Cancelled In Period (11,250)  
Number of warrants, Outstanding 3,445,666 3,648,541
Weighted Average Exercise Price [Abstract]    
Class of Warrant or Right, Exercise Price of Warrants or Rights $ 9.75  
Class Of Warrants Or Right, Exercise Price Of Warrants Grant In Period 0  
Class Of Warrants Or Right, Exercise Price Of Warrants Exercised In Period 7.55  
Class Of Warrants Or Right, Exercise Price Of Warrants Forfeited In Period 0  
Class of Warrant or Right, Exercise Price of Warrants or Rights $ 9.88 $ 9.75
Weighted Average Remaining Contractual Term Years [Abstract]    
Class Of Warrant Or Rights Grant In Period Weighted Average Remaining Contractual Term 0 years  
Class Of Warrant Or Rights Exercised Weighted Average Remaining Contractual Term 0 years  
Class Of Warrant Or Rights Forfeited Weighted Average Remaining Contractual Term 0 years  
Class Of Warrant Or Rights Outstanding Weighted Average Remaining Contractual Term 3 years 8 months 8 days 3 years 8 months 26 days
Aggregate Intrinsic Value [Abstract]    
Class Of Warrants Or Right, Outstanding, Aggregate Intrinsic Value $ 14.25  
Class Of Warrants Or Right, Grant In Period, Aggregate Intrinsic Value 0  
Class Of Warrants Or Right, Exercises In Period, Aggregate Intrinsic Value 9.96  
Class Of Warrants Or Right, Forfeitures In Period, Aggregate Intrinsic Value 0  
Class Of Warrants Or Right, Outstanding, Aggregate Intrinsic Value $ 6.07 $ 14.25