Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Unpaid Principal Balance
Impaired loans with no related allowance	$ 23,500		$ 23,500		$ 9,955
Impaired loans with related allowance	38,772		38,772		5,139
Total Impaired Loans	62,272		62,272		15,094
Recorded Investment
Impaired loans with no related allowance	14,662		14,662		7,352
Impaired loans with related allowance	37,822		37,822		4,357
Total Impaired Loans	52,484		52,484		11,709
Related Allowance	9,139		9,139		689
Average Recorded Investment
Impaired loans with no related allowance	19,498	$ 10,153	20,346	$ 11,075
Impaired loans with related allowance	37,811	6,175	38,000	6,226
Total Impaired Loans	57,309	16,328	58,346	17,301
Interest Income Recognized
Impaired loans with no related allowance	38	39	115	119
Impaired loans with related allowance	22	18	64	56
Total Impaired Loans	60	57	179	175
Commercial and industrial loans
Unpaid Principal Balance
Impaired loans with no related allowance	10,975		10,975		320
Impaired loans with related allowance	1,019		1,019
Recorded Investment
Impaired loans with no related allowance	3,819		3,819		320
Impaired loans with related allowance	1,018		1,018
Related Allowance	601		601
Average Recorded Investment
Impaired loans with no related allowance	8,625	877	9,225	881
Impaired loans with related allowance	1,018	329	1,018	329
Interest Income Recognized
Impaired loans with no related allowance	0	0	0	0
Impaired loans with related allowance	0		0	0
Agricultural production financing and other loans to farmers
Unpaid Principal Balance
Impaired loans with no related allowance	63		63		299
Recorded Investment
Impaired loans with no related allowance	0		0		137
Average Recorded Investment
Impaired loans with no related allowance		1,012		1,014
Impaired loans with related allowance		2,100		2,123
Interest Income Recognized
Impaired loans with no related allowance		0		0
Construction
Unpaid Principal Balance
Impaired loans with no related allowance					1,206
Recorded Investment
Impaired loans with no related allowance					970
Average Recorded Investment
Impaired loans with no related allowance		0		339
Interest Income Recognized
Impaired loans with no related allowance		0		0
Commercial and farmland
Unpaid Principal Balance
Impaired loans with no related allowance	12,385		12,385		8,037
Impaired loans with related allowance	34,207		34,207		2,648
Recorded Investment
Impaired loans with no related allowance	10,782		10,782		5,849
Impaired loans with related allowance	33,421		33,421		1,909
Related Allowance	7,981		7,981		231
Average Recorded Investment
Impaired loans with no related allowance	10,812	8,075	11,059	8,651
Impaired loans with related allowance	33,390	1,324	33,543	1,324
Interest Income Recognized
Impaired loans with no related allowance	37	39	113	117
Impaired loans with related allowance				0
Residential
Unpaid Principal Balance
Impaired loans with no related allowance	74		74		93
Impaired loans with related allowance	3,045		3,045		2,070
Recorded Investment
Impaired loans with no related allowance	58		58		76
Impaired loans with related allowance	2,908		2,908		2,044
Related Allowance	475		475		383
Average Recorded Investment
Impaired loans with no related allowance	58	189	59	190
Impaired loans with related allowance	2,921	2,072	2,951	2,095
Interest Income Recognized
Impaired loans with no related allowance	1	0	2	2
Impaired loans with related allowance	18	15	53	47
Home equity
Unpaid Principal Balance
Impaired loans with related allowance	501		501		417
Recorded Investment
Impaired loans with related allowance	475		475		400
Related Allowance	82		82		75
Average Recorded Investment
Impaired loans with related allowance	482	346	488	350
Interest Income Recognized
Impaired loans with related allowance	4	3	11	9
Individuals' loans for household and other personal expenditures
Unpaid Principal Balance
Impaired loans with no related allowance	3		3
Impaired loans with related allowance					4
Recorded Investment
Impaired loans with no related allowance	3		3
Impaired loans with related allowance					4
Related Allowance					$ 0
Average Recorded Investment
Impaired loans with no related allowance	$ 3		3
Impaired loans with related allowance		$ 4		5
Interest Income Recognized
Impaired loans with no related allowance			$ 0
Impaired loans with related allowance				$ 0