Share-Based Compensation - Components of Share Based Compensation Awards (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-tax compensation expense	$ 1,492	$ 1,315	$ 1,750
Income tax benefit	(451)	(392)	(462)
Share-based compensation expense, net of income taxes	1,041	923	1,288
Stock and ESPP Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-tax compensation expense	284	237	632
Income tax benefit	(23)	(21)	(71)
Share-based compensation expense, net of income taxes	261	216	561
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-tax compensation expense	1,208	1,078	1,118
Income tax benefit	(428)	(371)	(391)
Share-based compensation expense, net of income taxes	$ 780	$ 707	$ 727