Stock-Based Incentive Plan - Status of Options Granted Under Long-Term Incentive Plan (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Shares Under Option
Shares Under Option, Outstanding, Beginning balance | shares	504,908
Shares Under Option, Granted | shares	189,797
Shares Under Option, Expired | shares	(73,600)
Shares Under Option, Forfeited | shares	(16,000)
Shares Under Option, Exercised | shares	(92,370)
Share Under Option, Outstanding, Ending balance | shares	512,735
Shares Under Options, Exercisable at December 31 | shares	160,593
Weighted Average Exercise Price Per Share [Abstract]
Weighted Average Exercise Price Per Share, Outstanding, Beginning balance | $ / shares	$ 19.06
Weighted Average Exercise Price Per Share, Granted | $ / shares	28.15
Weighted Average Exercise Price Per Share, Expired | $ / shares	22.69
Weighted Average Exercise Price Per Share, Forfeited | $ / shares	23.35
Weighted Average Exercise Price Per Share, Exercised | $ / shares	18.14
Weighted Average Exercise Price Per Share, Outstanding, Ending balance | $ / shares	21.90
Weighted Average Exercise Price Per Share, Exercisable at December 31, 2016 | $ / shares	$ 17.80
Weighted Average Remaining Contractual Life, Outstanding at December 31, 2016	7 years 4 months 24 days
Weighted Average Remaining Contractual Life, Exercisable at December 31, 2016	5 years 7 months 6 days
Aggregate Intrinsic Value, Outstanding at December 31, 2017 | $	$ 3,170
Aggregate Intrinsic Value, Exercisable at December 31, 2017 | $	$ 1,646