Quarterly Financial Data (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total interest and dividend income	$ 40,608	$ 40,085	$ 38,282	$ 36,753	$ 36,344	$ 34,040	$ 32,099	$ 29,387	$ 155,728	$ 131,870	$ 108,874
Net interest income	29,745	29,901	28,794	27,758	28,116	26,878	25,826	24,100	116,198	104,920	91,509
Provision for loan losses	812	2,118	1,788	1,306	1,441	1,095	1,905	1,631	6,024	6,072	6,655
Non-interest income	6,754	6,276	6,792	6,153	4,433	5,933	5,606	4,751	25,975	20,723	21,435
Non-interest expense	22,905	21,444	21,984	21,175	20,006	20,794	19,543	18,999	87,508	79,342	70,037
Net income	$ 10,484	$ 10,357	$ 9,767	$ 9,473	$ 8,945	$ 9,236	$ 8,441	$ 7,097	$ 40,081	$ 33,719	$ 23,860
Basic earnings per common share (in dollars per share)	$ 0.69	$ 0.68	$ 0.64	$ 0.62	$ 0.59	$ 0.60	$ 0.55	$ 0.46	$ 2.63	$ 2.21	$ 1.57
Diluted earnings per common share (in dollars per share)	$ 0.69	$ 0.68	$ 0.64	$ 0.62	$ 0.59	$ 0.60	$ 0.55	$ 0.46	$ 2.63	$ 2.21	$ 1.57