Selected Quarterly Consolidated Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income	$ 47,517	$ 45,164	$ 43,286	$ 40,440	$ 38,900	$ 37,869	$ 37,153	$ 35,664	$ 176,407	$ 149,586	$ 133,470
Interest expense	13,639	11,715	10,175	8,588	8,011	7,810	7,249	6,985	44,117	30,055	22,992
Net interest income	33,878	33,449	33,111	31,852	30,889	30,059	29,904	28,679	132,290	119,531	110,478
Provision for loan losses	800	350	400	0	200	1,300	700	400	1,550	2,600	5,650
Net interest income after provision for loan losses	33,078	33,099	32,711	31,852	30,689	28,759	29,204	28,279	130,740	116,931	104,828
Noninterest income	15,163	15,215	15,993	15,743	16,210	17,283	16,806	14,510	62,114	64,809	65,129
Noninterest expense	26,682	26,062	26,288	27,130	25,754	26,754	26,306	25,286	106,162	104,100	101,103
Income before income taxes	21,559	22,252	22,416	20,465	21,145	19,288	19,704	17,503	86,692	77,640	68,854
Income tax expense	4,523	4,741	4,742	4,254	13,163	6,326	6,505	5,721	18,260	31,715	22,373
Net income	17,036	17,511	17,674	16,211	7,982	12,962	13,199	11,782	68,432	45,925	46,481
Net income available to common shareholders	$ 17,004	$ 17,475	$ 17,636	$ 16,173	$ 7,958	$ 12,934	$ 13,170	$ 11,755	$ 68,288	$ 45,817	$ 46,384
Weighted average common shares outstanding - basic	17,297	17,283	17,272	17,234	17,223	17,212	17,206	17,186	17,272	17,207	17,081
Weighted average common shares outstanding - diluted	17,385	17,382	17,387	17,345	17,349	17,318	17,316	17,293	17,391	17,338	17,208
Basic earnings per common share (in dollars per share)	$ 0.98	$ 1.01	$ 1.02	$ 0.94	$ 0.46	$ 0.75	$ 0.77	$ 0.68	$ 3.95	$ 2.66	$ 2.72
Diluted earnings per common share (in dollars per share)	0.98	1.01	1.01	0.93	0.46	0.75	0.76	0.68	3.93	2.64	2.70
Cash dividends declared per share (in dollars per share)	$ 0.47	$ 0.43	$ 0.43	$ 0.43	$ 0.39	$ 0.39	$ 0.38	$ 0.38	$ 1.76	$ 1.54	$ 1.46