Quarterly Financial Data (Unaudited) - Unaudited Quarterly Results of Operations (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]
Total interest and dividend income	$ 22,495	$ 21,532	$ 21,418	$ 21,437	$ 20,489	$ 17,465	$ 16,758	$ 16,704	$ 86,882	$ 71,416	$ 68,129
Net interest income	19,432	18,440	18,443	18,280	17,279	14,648	13,826	13,451	74,595	59,204	53,209
Provision for loan losses	282	1,038	1,501	1,019	1,247	846	3,115	930	3,840	6,138	6,381
Non-interest income	4,106	3,496	3,514	3,205	3,676	3,248	3,771	3,071	14,321	13,766	12,664
Non-interest expense	13,669	13,150	12,608	13,261	12,995	10,343	10,793	9,682	52,688	43,813	35,945
Net income	$ 6,743	$ 5,548	$ 5,617	$ 5,166	$ 4,728	$ 4,703	$ 2,951	$ 4,297	$ 23,074	$ 16,679	$ 17,136
Net income per share, basic	$ 0.47	$ 0.39	$ 0.39	$ 0.36	$ 0.33	$ 0.38	$ 0.24	$ 0.34	$ 1.60	$ 1.29	$ 1.38
Net income per share, diluted	$ 0.47	$ 0.39	$ 0.39	$ 0.36	$ 0.33	$ 0.38	$ 0.24	$ 0.34	$ 1.60	$ 1.29	$ 1.38