Stock-Based Incentive Plan - Status of Options Granted Under Long-Term Incentive Plan (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Shares Under Option
Shares Under Option, Outstanding, Beginning balance | shares	512,735
Shares Under Option, Granted | shares	192,278
Shares Under Option, Expired | shares	(500)
Shares Under Option, Forfeited | shares	(20,418)
Shares Under Option, Exercised | shares	(59,750)
Share Under Option, Outstanding, Ending balance | shares	624,345
Shares Under Options, Exercisable at September 30, 2018 | shares	259,031
Weighted Average Exercise Price Per Share [Abstract]
Weighted Average Exercise Price Per Share, Outstanding, Beginning balance | $ / shares	$ 21.90
Weighted Average Exercise Price Per Share, Granted | $ / shares	28.50
Weighted Average Exercise Price Per Share, Expired | $ / shares	28.15
Weighted Average Exercise Price Per Share, Forfeited | $ / shares	26.14
Weighted Average Exercise Price Per Share, Exercised | $ / shares	18.92
Weighted Average Exercise Price Per Share, Outstanding, Ending balance | $ / shares	24.08
Weighted Average Exercise Price Per Share, Exercisable at September 30, 2018 | $ / shares	$ 20.41
Weighted Average Remaining Contractual Life, Outstanding at September 30, 2018	7 years 6 months
Weighted Average Remaining Contractual Life, Exercisable at September 30, 2018	5 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding at September 30, 2018 | $	$ 2,150
Aggregate Intrinsic Value, Exercisable at September 30, 2018 | $	$ 1,662