Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic earnings per common share computation
NET INCOME	$ 5,548	$ 4,703	$ 16,331	$ 11,951
Net earnings allocated to participating securities	(23)	(21)	(70)	(56)
Net earnings allocated to common stock	5,525	4,682	16,261	11,895
Weighted average common shares outstanding, including shares considered participating securities	14,368	12,513	14,421	12,505
Less: Average participating securities	(53)	(51)	(55)	(52)
Weighted average shares	14,315	12,462	14,366	12,453
Basic earnings per common share	$ 0.39	$ 0.38	$ 1.13	$ 0.96
Diluted earnings per common share computation
Net earnings allocated to common stock	5,525	4,682	16,261	11,895
Weighted average common shares outstanding for basic earnings per common share	14,315	12,462	14,366	12,453
Add: Dilutive effects of assumed exercises of stock options	1	2	1	1
Weighted average shares and dilutive potential common shares	14,316	12,464	14,367	12,454
Diluted earnings per common share	$ 0.39	$ 0.38	$ 1.13	$ 0.96
Distributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation
Net earnings allocated to common stock	2,359	2,054	7,109	6,161
Undistributed Earnings Allocated to Common Stock [Member]
Basic earnings per common share computation
Net earnings allocated to common stock	$ 3,166	$ 2,628	$ 9,152	$ 5,734