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Summary of Stock Option (Detail)
 9 Months Ended
Sep. 30, 2018
USD ($)
$ / shares
shares
Options  
Beginning balance | shares 1,456,200
Grants | shares 205,750
Exercises | shares (31,000)
Cancellations | shares (15,250)
Expirations | shares (14,250)
Ending balance | shares 1,601,450
Options exercisable at End of Period | shares 1,281,020
Weighted-average exercise price  
Beginning balance | $ / shares $ 13.64
Grants | $ / shares 13.56
Exercises | $ / shares 4.60
Cancellations | $ / shares 17.66
Expirations | $ / shares 17.39
Ending balance | $ / shares 13.73
Options exercisable at End of Period | $ / shares $ 13.53
Weighted-average remaining contractual life (years)  
Options outstanding, Ending balance 4 years 4 months 24 days
Options exercisable, Ending balance 3 years 4 months 24 days
Aggregate intrinsic value  
Options outstanding, end of period | $ $ 695,000
Options exercisable, end of period | $ $ 695,000