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Summary of Stock Option (Detail)
 3 Months Ended
Mar. 31, 2017
USD ($)
$ / shares
shares
Options  
Beginning balance | shares 1,775,400
Grants | shares 75,000
Exercises | shares (6,000)
Cancellations | shares (11,200)
Ending balance | shares 1,833,200
Options exercisable at End of Period | shares 1,463,967
Weighted-average exercise price  
Beginning balance | $ / shares $ 13.44
Grants | $ / shares 16.60
Exercises | $ / shares 15.30
Cancellations | $ / shares 16.06
Ending balance | $ / shares 13.54
Options exercisable at End of Period | $ / shares $ 12.84
Weighted-average remaining contractual life (years)  
Options outstanding, Ending balance 4 years 7 months 6 days
Options exercisable, Ending balance 3 years 10 months 24 days
Aggregate intrinsic value  
Options outstanding, end of period | $ $ 12,092,000
Options exercisable, end of period | $ $ 10,695,000