Selected Consolidated Quarterly Financial Data - Summary of Consolidated Quarterly Financial Data (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 20,067	$ 20,142	$ 19,898	$ 19,746	$ 19,960	$ 19,984	$ 20,161	$ 20,052
Interest expense	2,043	2,042	1,739	1,681	1,709	2,440	2,617	2,862	7,505	9,628	14,103
Net interest income	18,024	18,100	18,159	18,065	18,251	17,544	17,544	17,190	72,348	70,529	73,512
Provision for loan losses	825	1,000	275	530	200	700	800	1,100
Net interest income after provision for loan losses	17,199	17,100	17,884	17,535	18,051	16,844	16,744	16,090	69,718	67,729	65,612
Other income	4,620	5,286	4,830	3,841	4,283	4,566	4,741	3,409
Operating expenses	14,396	14,431	14,830	14,107	19,611	13,784	13,724	12,666	57,764	59,244	52,389
Income before provision for income taxes	7,423	7,955	7,884	7,269	2,723	7,626	7,761	6,833
Provision for income taxes	2,491	2,790	2,767	2,563	784	2,658	2,774	2,397	10,611	8,613	10,927
Net income	$ 4,932	$ 5,165	$ 5,117	$ 4,706	$ 1,939	$ 4,968	$ 4,987	$ 4,436	$ 19,920	$ 16,330	$ 20,020
Basic earnings per share	$ 0.30	$ 0.31	$ 0.31	$ 0.27	$ 0.12	$ 0.29	$ 0.29	$ 0.26	$ 1.19	$ 0.96	$ 1.13
Diluted earnings per share	$ 0.30	$ 0.31	$ 0.30	$ 0.28	$ 0.11	$ 0.29	$ 0.29	$ 0.26	$ 1.19	$ 0.95	$ 1.12