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Summary of Stock Options Summarized by Exercise Price (Detail) - Incentive Stock Options - $ / shares
3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Outstanding Weighted Average, Shares 431,860  
Outstanding Weighted Average, Remaining Life (Months) 51 months  
Outstanding Weighted Average, Exercise Price $ 9.19 $ 9.38
Range One    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Exercise Price Per Share, Lower Range $ 7.50  
Outstanding Weighted Average, Shares 249,050  
Outstanding Weighted Average, Remaining Life (Months) 32 months  
Outstanding Weighted Average, Exercise Price $ 7.5  
Range Two    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Exercise Price Per Share, Lower Range 11.32  
Exercise Price Per Share, Upper Range $ 14.49  
Outstanding Weighted Average, Shares 182,810  
Outstanding Weighted Average, Remaining Life (Months) 77 months  
Outstanding Weighted Average, Exercise Price $ 11.49