Quarterly Financial Data (Unaudited) - Unaudited Quarterly Results of Operations (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]
Total interest and dividend income	$ 21,994	$ 22,237	$ 21,306	$ 21,641	$ 22,495	$ 21,532	$ 21,418	$ 21,437	$ 87,178	$ 86,882	$ 71,416
Net interest income	18,928	19,038	18,151	18,590	19,432	18,440	18,443	18,280	74,707	74,595	59,204
Provision for loan losses	668	463	486	943	282	1,038	1,501	1,019	2,560	3,840	6,138
Non-interest income	4,146	3,415	4,141	3,097	4,106	3,496	3,514	3,205	14,799	14,321	13,766
Non-interest expense	14,816	14,427	14,121	13,093	13,669	13,150	12,608	13,261	56,457	52,688	43,813
Net income	$ 5,508	$ 5,522	$ 5,602	$ 5,565	$ 6,743	$ 5,548	$ 5,617	$ 5,166	$ 22,197	$ 23,074	$ 16,679
Net income per share, basic	$ 0.38	$ 0.38	$ 0.39	$ 0.39	$ 0.47	$ 0.39	$ 0.39	$ 0.36	$ 1.54	$ 1.60	$ 1.29
Net income per share, diluted	$ 0.38	$ 0.38	$ 0.39	$ 0.39	$ 0.47	$ 0.39	$ 0.39	$ 0.36	$ 1.54	$ 1.60	$ 1.29