Components of Share Based Compensation Awards (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-tax compensation expense	$ 374	$ 326
Income tax benefit	(119)	(106)
Share-based compensation expense, net of income taxes	255	220
Stock and ESPP Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-tax compensation expense	38	46
Income tax benefit	(2)
Share-based compensation expense, net of income taxes	36	46
Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pre-tax compensation expense	336	280
Income tax benefit	(117)	(106)
Share-based compensation expense, net of income taxes	$ 219	$ 174