Stock-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Beginning balance, options	427,370
Granted, options	56,150
Exercised, options	(141,500)
Forfeited, options	(7,020)
Ending balance, options	335,000
Exercisable options, ending balance	25,280
Beginning balance, weighted average exercise price | $ / shares	$ 32.15
Ending balance, weighted average exercise price | $ / shares	34.75
Exercisable, weighted average exercisable price | $ / shares	$ 34.38
Outstanding, weighted average remaining contractual life (years)	5 years
Exercisable, weighted average remaining contractual life (years)	4 years 7 months 6 days
Outstanding, aggregate intrinsic value | $	$ 10,400
Exercisable, aggregate intrinsic value | $	$ 920