Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Basic earnings per common share computation:
Net income per consolidated statements of income	$ 5,019	$ 5,565
Net earnings allocated to participating securities	(31)	(29)
Net earnings allocated to common stock	$ 4,988	$ 5,536
Weighted average common shares outstanding, including shares considered participating securities	14,436	14,424
Less: Average participating securities	(79)	(67)
Weighted average shares	14,357	14,357
Basic earnings per common share	$ 0.35	$ 0.39
Diluted earnings per common share computation:
Net earnings allocated to common stock	$ 4,988	$ 5,536
Weighted average common shares outstanding for basic earnings per common share	14,357	14,357
Add: Dilutive effects of assumed exercises of stock options	0	0
Weighted average shares and dilutive potential common shares	14,357	14,357
Diluted earnings per common share	$ 0.35	$ 0.39
Distributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 2,369	$ 2,370
Undistributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 2,619	$ 3,166