Stock-Based Incentive Plan - Status of Options Granted Under Long-Term Incentive Plan (Detail) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Shares Under Option
Shares Under Option, Outstanding, Beginning balance | shares	504,908
Shares Under Option, Granted | shares	191,297
Shares Under Option, Expired | shares	(73,000)
Shares Under Option, Forfeited | shares	(6,500)
Shares Under Option, Exercised | shares	(73,870)
Share Under Option, Outstanding, Ending balance | shares	542,835
Shares Under Options, Exercisable at June 30, 2017 | shares	177,025
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	22.70
Weighted Average Exercise Price Per Share, Forfeited | $ / shares	23.34
Weighted Average Exercise Price Per Share, Exercised | $ / shares	17.97
Weighted Average Exercise Price Per Share, Outstanding, Ending balance | $ / shares	21.84
Weighted Average Exercise Price Per Share, Exercisable at June 30, 2017 | $ / shares	$ 17.87
Weighted Average Remaining Contractual Life, Outstanding at June 30, 2017	7 years 9 months 18 days
Weighted Average Remaining Contractual Life, Exercisable at June 30, 2017	5 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding at June 30, 2017 | $	$ 4,403
Aggregate Intrinsic Value, Exercisable at June 30, 2017 | $	$ 2,138