Earnings Per Share - Summary of Components Comprising Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basic EPS Computation:
Numerator - Earnings available to common stockholders	$ 6,201	$ 5,154	$ 11,817	$ 9,326
Denominator - Weighted average number of common shares outstanding	7,610,002	7,534,761	7,603,734	7,528,555
Basic earnings per common share	$ 0.81	$ 0.68	$ 1.55	$ 1.24
Diluted EPS Computation:
Numerator - Earnings available to common stockholders	$ 6,201	$ 5,154	$ 11,817	$ 9,326
Denominator - Weighted average number of common shares outstanding	7,610,002	7,534,761	7,603,734	7,528,555
Dilutive effect of stock options	3,366	4,471	3,451	4,486
Weighted average number of shares outstanding-diluted	7,613,368	7,539,232	7,607,185	7,533,041
Diluted earnings per common share	$ 0.81	$ 0.68	$ 1.55	$ 1.24