Schedule of Employee Stock Purchase Plan (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]
Number of ESPP shares issued	44,470	42,443	56,279
Amount of proceeds received from employees	$ 1,337	$ 1,288	$ 1,207
Share-based compensation expense	$ 333	$ 352	$ 332