Earnings Per Share - Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share Basic And Diluted [Abstract]
Numerator for basic and diluted earnings per share - income available to common shareholders	$ 6,039	$ 5,770	$ 16,267	$ 15,796
Denominator for basic earnings per share - weighted-average shares outstanding	16,658	16,760	16,714	16,760
Effect of dilutive securities - employee stock options and awards	84	60	61	49
Denominator for diluted earnings per share - adjusted weighted-average shares outstanding	16,742	16,820	16,775	16,809
Basic earnings per share	$ 0.36	$ 0.34	$ 0.97	$ 0.94
Diluted earnings per share	$ 0.36	$ 0.34	$ 0.97	$ 0.94
Average anti-dilutive options and awards excluded from computation of diluted earnings per share	470	588	567	579