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Summary of Stock Option (Detail)
 6 Months Ended
Jun. 30, 2017
USD ($)
$ / shares
shares
Options  
Beginning balance | shares 1,775,400
Grants | shares 125,750
Exercises | shares (130,250)
Cancellations | shares (24,700)
Expirations | shares (7,000)
Ending balance | shares 1,739,200
Options exercisable at End of Period | shares 1,468,506
Weighted-average exercise price  
Beginning balance | $ / shares $ 13.44
Grants | $ / shares 17.38
Exercises | $ / shares 12.12
Cancellations | $ / shares 15.98
Expirations | $ / shares 22.66
Ending balance | $ / shares 13.75
Options exercisable at End of Period | $ / shares $ 13.17
Weighted-average remaining contractual life (years)  
Options outstanding, Ending balance 4 years 7 months 6 days
Options exercisable, Ending balance 4 years
Aggregate intrinsic value  
Options outstanding, end of period | $ $ 8,114,000
Options exercisable, end of period | $ $ 7,694,000