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, 2018 USD ($) $ / shares shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding, beginning of year, Shares | shares	1,325,965
Granted, Shares | shares	0
Exercised, Shares | shares	(173,822)
Cancelled, Shares | shares	(66,600)
Outstanding, end of year, Shares | shares	1,085,543
Exercisable at end of year, Shares | shares	407,463
Outstanding, beginning of year, Weighted-Average Ex. Price | $ / shares	$ 33.01
Granted, Weighted-Average Ex. Price | $ / shares	0
Exercised, Weighted-Average Ex. Price | $ / shares	22.23
Cancelled, Weighted-Average Ex. Price | $ / shares	36.25
Outstanding, end of year, Weighted-Average Ex. Price | $ / shares	34.54
Exercisable at end of year, Weighted-Average Ex. Price | $ / shares	$ 27.41
Outstanding, end of year, Weighted-Average Remaining Contractual Term (Years)	6 years 6 months 18 days
Exercisable at end of year, Weighted-Average Remaining Contractual Term (Years)	4 years 7 months 24 days
Outstanding, end of year, Aggregate Intrinsic Value | $	$ 25,135
Exercisable at end of year, Aggregate Intrinsic Value | $	$ 12,337