Stock-Based Compensation - Stock-Based Employee Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Labor And Related Expense [Abstract]
Stock-based compensation expense	$ 1,180	$ 1,636	$ 1,717
Tax benefit	301	633	664
Stock-based compensation expense, net of tax	$ 879	$ 1,003	$ 1,053