Stock-Based Incentive Plan - Compensation Expense Related to Stock Incentive Plans Recognized (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Stock-based compensation expense:
Total Expense	$ 2,430	$ 2,597
Tax benefit on nonqualified stock option expense, restricted stock awards and disqualifying dispositions of incentive stock options	624	1,263
Stock Options [Member]
Stock-based compensation expense:
Total Expense	797	678
Restricted Stock Awards [Member]
Stock-based compensation expense:
Total Expense	1,582	1,872
Employee Stock Purchase Plan [Member]
Stock-based compensation expense:
Total Expense	$ 51	$ 47