Annual report pursuant to Section 13 and 15(d)

Stock Option and Purchase Plans - Compensation Expense Information Based on Fair Value of Stock Options (Detail)

v3.8.0.1
Stock Option and Purchase Plans - Compensation Expense Information Based on Fair Value of Stock Options (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Stock Compensation Expense $ 2,598 $ 2,281 $ 2,274
Tax Benefit (140) (145) (177)
Stock Compensation Expense, Net of Tax $ 2,458 $ 2,136 $ 2,097