Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic earnings per common share computation:
Net income per consolidated statements of income	$ 6,416	$ 5,522	$ 15,500	$ 16,689
Net earnings allocated to participating securities	(40)	(30)	(101)	(92)
Net earnings allocated to common stock	$ 6,376	$ 5,492	$ 15,399	$ 16,597
Weighted average common shares outstanding, including shares considered participating securities	14,464	14,406	14,453	14,408
Less: Average participating securities	(82)	(71)	(85)	(72)
Weighted average shares	14,382	14,335	14,368	14,336
Basic earnings per common share	$ 0.44	$ 0.38	$ 1.07	$ 1.16
Diluted earnings per common share computation:
Net earnings allocated to common stock	$ 6,376	$ 5,492	$ 15,399	$ 16,597
Weighted average shares and dilutive potential common shares	14,382	14,335	14,368	14,336
Diluted earnings per common share	$ 0.44	$ 0.38	$ 1.07	$ 1.16
Distributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 2,370	$ 2,363	$ 7,107	$ 7,095
Undistributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation:
Net earnings allocated to common stock	$ 4,006	$ 3,129	$ 8,292	$ 9,502