Calculation of Basic and Diluted Earnings per Share (Detail) (USD $) In Thousands, except 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 [Line Items]
Net income available to common shareholders	$ 6,401	$ 5,425	$ 17,973	$ 15,843
Denominator for basic earnings per share - weighted average shares outstanding	13,336,799	13,149,050	13,274,801	13,067,551
Effect of dilutive common shares	275,343	146,377	244,302	133,799
Denominator for diluted earnings per share - adjusted weighted average shares outstanding	13,612,142	13,295,427	13,519,103	13,201,350
Basic earnings per share	$ 0.48	$ 0.41	$ 1.35	$ 1.21
Diluted earnings per share	$ 0.47	$ 0.41	$ 1.33	$ 1.20
Antidilutive shares excluded from computation of average dilutive earnings per share		227,139	123,882	349,649