Quarterly Condensed Statements of Income-Unaudited (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
Quarterly Condensed Statements of Income-Unaudited
Total interest income	$ 23,462	$ 23,691	$ 22,651	$ 22,744	$ 22,446	$ 22,703	$ 22,423	$ 22,021	$ 92,548	$ 89,593	$ 89,439
Net interest income after provision for loan losses	17,172	18,488	17,987	16,868	15,451	15,777	16,978	15,351	70,515	63,557	62,431
Other income	5,444	6,627	7,241	6,446	6,708	6,842	7,412	6,270	25,758	27,232	26,047
Other Noninterest Expense	17,758	18,674	18,761	18,539	18,080	18,371	18,403	17,969	23,421	21,496	20,987
Income before income taxes	4,858	6,441	6,467	4,775	4,079	4,248	5,987	3,652	22,541	17,966	17,918
Net income	$ 3,957	$ 5,101	$ 5,070	$ 3,892	$ (3,315)	$ 3,017	$ 4,139	$ 2,731	$ 18,020	$ 6,572	$ 13,459
Earnings per common share - assuming dilution	$ 1.13	$ 1.46	$ 1.45	$ 1.11	$ (0.95)	$ 0.87	$ 1.19	$ 0.78	$ 5.15	$ 1.88	$ 3.89
Dividends declared per common share (in dollars per share)	$ 0.37	$ 0.36	$ 0.34	$ 0.34	$ 0.34	$ 0.33	$ 0.33	$ 0.33	$ 1.41	$ 1.33	$ 1.29