Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unpaid Principal Balance
Impaired loans with no related allowance	$ 14,555	$ 25,979	$ 29,365
Impaired loans with related allowance	10,501	6,123	6,155
Total Impaired Loans	25,056	32,102	35,520
Recorded Investment
Impaired loans with no related allowance	11,594	17,931	21,227
Impaired loans with related allowance	10,431	5,280	4,788
Total Impaired Loans	22,025	23,211	26,015
Related Allowance	1,872	1,637	888
Average Recorded Investment
Impaired loans with no related allowance	15,824	22,752	22,775
Impaired loans with related allowance	10,448	6,135	4,818
Total Impaired Loans	26,272	28,887	27,593
Interest Income Recognized
Impaired loans with no related allowance	168	360	327
Impaired loans with related allowance	68	39	20
Total Impaired Loans	236	399	347
Commercial and industrial loans
Unpaid Principal Balance
Impaired loans with no related allowance	828	7,611	4,028
Impaired loans with related allowance		812
Recorded Investment
Impaired loans with no related allowance	806	1,536	1,696
Impaired loans with related allowance		782
Related Allowance		552
Average Recorded Investment
Impaired loans with no related allowance	833	3,839	1,770
Impaired loans with related allowance		1,517
Interest Income Recognized
Impaired loans with no related allowance			37
Impaired loans with related allowance
Agriculture production financing and other loans to farmers
Unpaid Principal Balance
Impaired loans with no related allowance	679	732	367
Impaired loans with related allowance		357	660
Recorded Investment
Impaired loans with no related allowance	679	700	338
Impaired loans with related allowance		327	660
Related Allowance		114	36
Average Recorded Investment
Impaired loans with no related allowance	679	762	357
Impaired loans with related allowance		327	690
Interest Income Recognized
Impaired loans with no related allowance
Impaired loans with related allowance
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	835
Impaired loans with related allowance	7,977
Interest Income Recognized
Impaired loans with no related allowance
Commercial and farmland
Unpaid Principal Balance
Impaired loans with no related allowance	11,176	16,758	22,828
Impaired loans with related allowance	171	2,988	4,237
Recorded Investment
Impaired loans with no related allowance	8,994	15,163	17,752
Impaired loans with related allowance	171	2,269	2,985
Related Allowance	6	567	553
Average Recorded Investment
Impaired loans with no related allowance	12,975	17,495	18,944
Impaired loans with related allowance	171	2,379	2,990
Interest Income Recognized
Impaired loans with no related allowance	165	360	288
Impaired loans with related allowance
Residential
Unpaid Principal Balance
Impaired loans with no related allowance	118	833	2,073
Impaired loans with related allowance	1,958	1,616	968
Recorded Investment
Impaired loans with no related allowance	100	519	1,402
Impaired loans with related allowance	1,907	1,572	877
Related Allowance	362	327	233
Average Recorded Investment
Impaired loans with no related allowance	101	635	1,665
Impaired loans with related allowance	1,915	1,580	872
Interest Income Recognized
Impaired loans with no related allowance	3		2
Impaired loans with related allowance	57	28	14
Home equity
Unpaid Principal Balance
Impaired loans with no related allowance	49	40	60
Impaired loans with related allowance	376	350	290
Recorded Investment
Impaired loans with no related allowance	48	8	30
Impaired loans with related allowance	358	330	266
Related Allowance	74	77	66
Average Recorded Investment
Impaired loans with no related allowance	48	14	30
Impaired loans with related allowance	365	332	266
Interest Income Recognized
Impaired loans with no related allowance
Impaired loans with related allowance	10	11	6
Individuals' loans for household and other personal expenditures
Unpaid Principal Balance
Impaired loans with no related allowance		5	9
Impaired loans with related allowance	18
Recorded Investment
Impaired loans with no related allowance		5	9
Impaired loans with related allowance	18
Related Allowance	1
Average Recorded Investment
Impaired loans with no related allowance		7	9
Impaired loans with related allowance	20
Interest Income Recognized
Impaired loans with no related allowance
Impaired loans with related allowance	1
Other commercial loans
Unpaid Principal Balance
Impaired loans with no related allowance	353
Recorded Investment
Impaired loans with no related allowance	353
Average Recorded Investment
Impaired loans with no related allowance	353
Interest Income Recognized
Impaired loans with no related allowance