Selected Consolidated Quarterly Financial Data - Summary of Consolidated Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Interest income	$ 23,149	$ 21,970	$ 20,576	$ 20,168	$ 20,067	$ 20,142	$ 19,898	$ 19,746
Interest expense	2,461	2,395	2,143	2,035	2,043	2,042	1,739	1,681	$ 9,034	$ 7,505	$ 9,628
Net interest income	20,688	19,575	18,433	18,133	18,024	18,100	18,159	18,065	76,829	72,348	70,529
Provision for loans losses	300	300	300	375	825	1,000	275	530
Net interest income after provision for loan losses	20,388	19,275	18,133	17,758	17,199	17,100	17,884	17,535	75,554	69,718	67,729
Other income	4,118	4,152	4,171	3,985	4,620	5,286	4,830	3,841
Operating expenses (excluding merger related expenses)	15,885	15,117	14,208	13,687	14,396	14,431	14,830	14,107	60,775	57,764	59,244
Merger related expenses	614	1,030	184	50					1,878
Income before provision for income taxes	8,007	7,280	7,912	8,006	7,423	7,955	7,884	7,269
Provision for income taxes	2,777	2,582	2,779	2,745	2,491	2,790	2,767	2,563	10,883	10,611	8,613
Net income	$ 5,230	$ 4,698	$ 5,133	$ 5,261	$ 4,932	$ 5,165	$ 5,117	$ 4,706	$ 20,322	$ 19,920	$ 16,330
Basic earnings per share	$ 0.31	$ 0.28	$ 0.31	$ 0.32	$ 0.30	$ 0.31	$ 0.31	$ 0.27	$ 1.22	$ 1.19	$ 0.96
Diluted earnings per share	$ 0.31	$ 0.28	$ 0.31	$ 0.31	$ 0.30	$ 0.31	$ 0.30	$ 0.28	$ 1.21	$ 1.19	$ 0.95