Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basic earnings per common share computation:
Net income per consolidated statements of income	$ 4,065	$ 5,602	$ 9,084	$ 11,167
Net earnings allocated to participating securities	(27)	(33)	(60)	(62)
Net earnings allocated to common stock	$ 4,038	$ 5,569	$ 9,024	$ 11,105
Weighted average common shares outstanding, including shares considered participating securities	14,460	14,404	14,448	14,410
Less: Average participating securities	(92)	(80)	(86)	(73)
Weighted average shares	14,368	14,324	14,362	14,337
Basic earnings per common share	$ 0.28	$ 0.39	$ 0.63	$ 0.77
Diluted earnings per common share computation:
Net earnings allocated to common stock	$ 4,038	$ 5,569	$ 9,024	$ 11,105
Weighted average shares and dilutive potential common shares	14,368	14,324	14,362	14,366
Diluted earnings per common share	$ 0.28	$ 0.39	$ 0.63	$ 0.77
Distributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 2,369	$ 2,362	$ 4,737	$ 4,731
Undistributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 1,669	$ 3,207	$ 4,287	$ 6,374