Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Unpaid Principal Balance
Impaired loans with no related allowance	$ 12,245		$ 12,245		$ 14,555
Impaired loans with related allowance	7,213		7,213		10,501
Total Impaired Loans	19,458		19,458		25,056
Recorded Investment
Impaired loans with no related allowance	10,125		10,125		11,594
Impaired loans with related allowance	6,149		6,149		10,431
Total Impaired Loans	16,274		16,274		22,025
Related Allowance	2,261		2,261		1,872
Average Recorded Investment
Impaired loans with no related allowance	10,153	$ 14,402	11,075	$ 15,370
Impaired loans with related allowance	6,175	2,161	6,226	2,179
Total Impaired Loans	16,328	16,563	17,301	17,549
Interest Income Recognized
Impaired loans with no related allowance	39	41	119	130
Impaired loans with related allowance	18	16	56	45
Total Impaired Loans	57	57	175	175
Commercial and industrial loans
Unpaid Principal Balance
Impaired loans with no related allowance	897		897		828
Impaired loans with related allowance	563		563
Recorded Investment
Impaired loans with no related allowance	877		877		806
Impaired loans with related allowance	329		329
Related Allowance	329		329
Average Recorded Investment
Impaired loans with no related allowance	877	979	881	994
Impaired loans with related allowance	329		329
Interest Income Recognized
Impaired loans with no related allowance	0	0	0	0
Impaired loans with related allowance	0		0
Agricultural production financing and other loans to farmers
Unpaid Principal Balance
Impaired loans with no related allowance	1,023		1,023		679
Impaired loans with related allowance	2,144		2,144
Recorded Investment
Impaired loans with no related allowance	1,012		1,012		679
Impaired loans with related allowance	2,092		2,092
Related Allowance	1,351		1,351
Average Recorded Investment
Impaired loans with no related allowance	1,012	640	1,014	640
Impaired loans with related allowance	2,100		2,123
Interest Income Recognized
Impaired loans with no related allowance	0	0	0	0
Impaired loans with related allowance	0		0
Construction
Unpaid Principal Balance
Impaired loans with no related allowance					1,352
Impaired loans with related allowance					7,978
Recorded Investment
Impaired loans with no related allowance					614
Impaired loans with related allowance					7,977
Related Allowance					1,429
Average Recorded Investment
Impaired loans with no related allowance	0	614	339	930
Interest Income Recognized
Impaired loans with no related allowance	0	0	0	0
Commercial and farmland
Unpaid Principal Balance
Impaired loans with no related allowance	10,118		10,118		11,176
Impaired loans with related allowance	2,061		2,061		171
Recorded Investment
Impaired loans with no related allowance	8,047		8,047		8,994
Impaired loans with related allowance	1,324		1,324		171
Related Allowance	124		124		6
Average Recorded Investment
Impaired loans with no related allowance	8,075	12,098	8,651	12,733
Impaired loans with related allowance	1,324		1,324
Interest Income Recognized
Impaired loans with no related allowance	39	40	117	128
Residential
Unpaid Principal Balance
Impaired loans with no related allowance	207		207		118
Impaired loans with related allowance	2,079		2,079		1,958
Recorded Investment
Impaired loans with no related allowance	189		189		100
Impaired loans with related allowance	2,055		2,055		1,907
Related Allowance	389		389		362
Average Recorded Investment
Impaired loans with no related allowance	189	62	190	63
Impaired loans with related allowance	2,072	1,797	2,095	1,812
Interest Income Recognized
Impaired loans with no related allowance	0	1	2	2
Impaired loans with related allowance	15	13	47	37
Home equity
Unpaid Principal Balance
Impaired loans with no related allowance					49
Impaired loans with related allowance	362		362		376
Recorded Investment
Impaired loans with no related allowance					48
Impaired loans with related allowance	345		345		358
Related Allowance	68		68		74
Average Recorded Investment
Impaired loans with related allowance	346	364	350	367
Interest Income Recognized
Impaired loans with related allowance	3	3	9	8
Individuals' loans for household and other personal expenditures
Unpaid Principal Balance
Impaired loans with related allowance	4		4		18
Recorded Investment
Impaired loans with related allowance	4		4		18
Related Allowance	0		0		1
Average Recorded Investment
Impaired loans with no related allowance		9		10
Impaired loans with related allowance	$ 4		5
Interest Income Recognized
Impaired loans with no related allowance		$ 0		$ 0
Impaired loans with related allowance			$ 0
Public finance and other commercial loans
Unpaid Principal Balance
Impaired loans with no related allowance					353
Recorded Investment
Impaired loans with no related allowance					$ 353