Earnings Per Share - Basic and diluted earnings per share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share Basic And Diluted [Abstract]
Numerator for basic and diluted earnings per share - income available to common shareholders	$ 4,830	$ 4,763	$ 10,228	$ 10,026
Denominator for basic earnings per share - weighted-average shares outstanding	16,696	16,770	16,742	16,760
Effect of dilutive securities - employee stock options and awards	51	3	54	3
Denominator for diluted earnings per share - adjusted weighted-average shares outstanding	16,747	16,773	16,796	16,763
Basic earnings per share	$ 0.29	$ 0.28	$ 0.61	$ 0.60
Diluted earnings per share	$ 0.29	$ 0.28	$ 0.61	$ 0.60
Average anti-dilutive options and awards excluded from computation of diluted earnings per share	668	603	661	589