Selected Quarterly Consolidated Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Interest and dividend income	$ 38,900	$ 37,869	$ 37,153	$ 35,664	$ 35,055	$ 33,256	$ 32,190	$ 32,969	$ 149,586	$ 133,470	$ 125,750
Interest expense	8,011	7,810	7,249	6,985	6,467	5,877	5,414	5,234	30,055	22,992	21,768
Net interest income	30,889	30,059	29,904	28,679	28,588	27,379	26,776	27,735	119,531	110,478	103,982
Provision for loan losses	200	1,300	700	400	2,900	1,800	450	500	2,600	5,650	1,050
Net interest income after provision for loan losses	30,689	28,759	29,204	28,279	25,688	25,579	26,326	27,235	116,931	104,828	102,932
Noninterest income	16,210	17,283	16,806	14,510	17,320	17,261	15,914	14,634	64,809	65,129	58,340
Noninterest expense	25,754	26,754	26,306	25,286	24,973	24,650	26,030	25,450	104,100	101,103	96,929
Income before income taxes	21,145	19,288	19,704	17,503	18,035	18,190	16,210	16,419	77,640	68,854	64,343
Income tax expense	13,163	6,326	6,505	5,721	5,873	5,863	5,153	5,484	31,715	22,373	20,878
Net income	$ 7,982	$ 12,962	$ 13,199	$ 11,782	$ 12,162	$ 12,327	$ 11,057	$ 10,935	$ 45,925	$ 46,481	$ 43,465
Weighted average common shares outstanding - basic	17,223	17,212	17,206	17,186	17,142	17,090	17,067	17,023	17,207	17,081	16,879
Weighted average common shares outstanding - diluted	17,349	17,318	17,316	17,293	17,245	17,203	17,194	17,157	17,338	17,208	17,067
Basic earnings per common share (in dollars per share)	$ 0.46	$ 0.75	$ 0.77	$ 0.68	$ 0.71	$ 0.72	$ 0.65	$ 0.64	$ 2.66	$ 2.72	$ 2.57
Diluted earnings per common share (in dollars per share)	0.46	0.75	0.76	0.68	0.70	0.72	0.64	0.64	2.64	2.70	2.54
Cash dividends declared per share (in dollars per share)	$ 0.39	$ 0.39	$ 0.38	$ 0.38	$ 0.37	$ 0.37	$ 0.36	$ 0.36	$ 1.54	$ 1.46	$ 1.36