Stock-Based Incentive Plan - Compensation Expense Related to Stock Incentive Plans Recognized (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation expense:
Total Expense	$ 2,597	$ 1,457
Tax benefit on nonqualified stock option expense, restricted stock awards and disqualifying dispositions of incentive stock options	1,263	407
Stock Options [Member]
Stock-based compensation expense:
Total Expense	678	463
Restricted Stock Awards [Member]
Stock-based compensation expense:
Total Expense	1,872	944
Employee Stock Purchase Plan [Member]
Stock-based compensation expense:
Total Expense	$ 47	$ 50