Quarterly Financial Data (unaudited) - Schedule of 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	$ 18,995	$ 19,219	$ 18,725	$ 18,946	$ 19,172	$ 19,457	$ 19,461	$ 19,489	$ 75,885	$ 77,579	$ 80,654
Interest expense	1,039	978	981	998	1,080	1,138	1,353	1,546	3,996	5,117	8,174
Net interest income	17,956	18,241	17,744	17,948	18,092	18,319	18,108	17,943	71,889	72,462	72,480
Provision for loan and lease losses	648	233	1,251	1,475	1,614	4,094	3,446	2,074	3,607	11,228	10,035
Net interest income after provision for loan and lease losses	17,308	18,008	16,493	16,473	16,478	14,225	14,662	15,869	68,282	61,234	62,445
Noninterest income	12,076	12,510	11,924	12,141	11,116	13,202	10,991	11,475	48,651	46,784	40,260
Total noninterest expense	22,562	22,019	21,790	20,883	21,623	19,988	19,286	20,236	87,254	81,133	76,282
Income before income taxes	6,822	8,499	6,627	7,731	5,971	7,439	6,367	7,108	29,679	26,885	26,423
Income taxes	1,632	2,264	1,547	2,005	1,049	1,400	1,537	1,710	7,448	5,696	5,551
Net income	$ 5,190	$ 6,235	$ 5,080	$ 5,726	$ 4,922	$ 6,039	$ 4,830	$ 5,398	$ 22,231	$ 21,189	$ 20,872
Net income per share:
Basic (in dollars per share)	$ 0.32	$ 0.38	$ 0.31	$ 0.35	$ 0.30	$ 0.36	$ 0.29	$ 0.32	$ 1.37	$ 1.28	$ 1.25
Diluted (in dollars per share)	$ 0.32	$ 0.38	$ 0.31	$ 0.35	$ 0.30	$ 0.36	$ 0.29	$ 0.32	$ 1.36	$ 1.27	$ 1.24
Dividends per share	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.20	$ 0.80	$ 0.80	$ 0.80