Segment and Related Information - Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Interest and dividend income	$ 65,325	$ 63,984	$ 62,143	$ 60,140	$ 59,029	$ 57,772	$ 56,342	$ 53,621	$ 251,592	$ 226,764	$ 202,739
Interest expense	12,089	10,821	9,429	7,453	7,060	6,772	6,041	5,587	39,792	25,460	22,103
Net Interest Income	53,236	53,163	52,714	52,687	51,969	51,000	50,301	48,034	211,800	201,304	180,636
Provision for loan and lease losses	2,058	272	1,045	567	2,014	402	976	769	3,942	4,161	4,321
Income before income tax expense	23,808	26,361	27,842	26,229	20,981	25,917	25,207	23,137	104,240	95,242	86,516
Net Income	$ 18,911	$ 20,902	$ 22,059	$ 20,436	$ 2,457	$ 17,394	$ 16,926	$ 15,717	$ 82,308	$ 52,494	$ 59,340
Net income per common share (basic) (in dollars per share)	$ 1.24	$ 1.37	$ 1.44	$ 1.34	$ 0.16	$ 1.14	$ 1.11	$ 1.04	$ 5.39	$ 3.46	$ 3.94
Net income per common share (diluted) (in dollars per share)	$ 1.23	$ 1.36	$ 1.43	$ 1.33	$ 0.16	$ 1.14	$ 1.11	$ 1.03	$ 5.35	$ 3.43	$ 3.91