Stock Option Plan and Restricted Stock Plan - Schedule of Analysis of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding, beginning of year, Shares | shares	1,094,035
Granted, Shares | shares	452,450
Exercised, Shares | shares	(140,250)
Cancelled, Shares | shares	(80,270)
Outstanding, end of year, Shares | shares	1,325,965
Exercisable at end of year, Shares | shares	458,715
Outstanding, beginning of year, Weighted-Average Ex. Price | $ / shares	$ 27.40
Granted, Weighted-Average Ex. Price | $ / shares	42.35
Exercised, Weighted-Average Ex. Price | $ / shares	20.92
Cancelled, Weighted-Average Ex. Price | $ / shares	30.33
Outstanding, end of year, Weighted-Average Ex. Price | $ / shares	33.01
Exercisable at end of year, Weighted-Average Ex. Price | $ / shares	$ 23.94
Outstanding, end of year, Weighted-Average Remaining Contractual Term (Years)	7 years 1 month 13 days
Exercisable at end of year, Weighted-Average Remaining Contractual Term (Years)	4 years 7 months 28 days
Outstanding, end of year, Aggregate Intrinsic Value | $	$ 15,966
Exercisable at end of year, Aggregate Intrinsic Value | $	$ 9,684