Summarized Quarterly Financial Information (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 income	$ 37,053	$ 36,366	$ 35,298	$ 34,214	$ 33,884	$ 33,046	$ 32,932	$ 32,289	$ 142,930	$ 132,152	$ 127,074
Taxable equivalent adjustment	(371)	(358)	(370)	(357)	(258)	(224)	(195)	(192)
Interest income (FTE)	37,424	36,724	35,668	34,571	34,142	33,270	33,127	32,481
Interest expense	4,664	4,340	4,036	3,767	3,504	3,268	3,264	3,169	16,805	13,207	11,830
Net Interest Income	32,760	32,384	31,632	30,804	30,638	30,002	29,863	29,312
Provision for loan losses	422	1,393	510	681	1,301	1,432	1,122	539	3,006	4,395	6,988
Investment securities gains (losses)	200	0	0	4,276	0	2,668	845	0
Noninterest income	15,367	14,611	14,921	14,231	14,371	14,079	13,736	13,127	63,607	58,825	67,206
Noninterest expense	22,893	24,309	24,176	24,600	22,456	25,284	24,283	24,140	95,981	96,164	92,951
Income before income tax expense	25,012	21,293	21,867	24,030	21,252	20,033	19,039	17,760	90,745	77,211	82,511
Income tax expense	14,972	7,003	6,812	7,647	6,338	6,577	6,303	5,866	36,435	25,083	28,414
Interest Income Taxable Equivalent Adjustment - Tax	371	358	370	357	258	224	195	192
Net Income Available to Common Shareholders	9,669	13,932	14,685	16,026	14,656	13,232	12,541	11,702	54,310	52,128	54,097
Net earnings allocated to common shareholders	$ 9,560	$ 13,778	$ 14,531	$ 15,849	$ 14,479	$ 13,075	$ 12,391	$ 11,571	$ 53,719	$ 51,505	$ 53,484
Basic earnings per common share	$ 0.62	$ 0.89	$ 0.94	$ 1.04	$ 0.97	$ 0.88	$ 0.83	$ 0.78	$ 3.49	$ 3.46	$ 3.54
Diluted earnings per common share	$ 0.62	$ 0.89	$ 0.94	$ 1.04	$ 0.97	$ 0.88	$ 0.83	$ 0.78	$ 3.48	$ 3.45	$ 3.53
Basic	15,472	15,485	15,462	15,252	14,894	14,899	14,889	14,916	15,412	14,900	15,123
Average shares outstanding, diluted	15,497	15,505	15,487	15,277	14,914	14,909	14,902	14,927	15,436	14,913	15,171