Stock Options and Restricted Stock - Weighted Average Grant Date Fair Values of Options Granted (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Cash received from option exercises		$ 837	$ 1,844
Total tax benefits realized for tax deductions from options exercised		833	2,109
Total intrinsic value of options exercised		2,967	6,969
Aggregate intrinsic value of vested options outstanding	$ 1,128	$ 1,073	$ 3,448