Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Unpaid Principal Balance
Impaired loans with no related allowance	$ 20,384		$ 20,384		$ 14,555
Impaired loans with related allowance	5,842		5,842		10,501
Total Impaired Loans	26,226		26,226		25,056
Recorded Investment
Impaired loans with no related allowance	16,471		16,471		11,594
Impaired loans with related allowance	5,502		5,502		10,431
Total Impaired Loans	21,973		21,973		22,025
Related Allowance	2,296		2,296		1,872
Average Recorded Investment
Impaired loans with no related allowance	17,433	$ 12,758	18,112	$ 13,128
Impaired loans with related allowance	5,600	2,124	5,634	2,137
Total Impaired Loans	23,033	14,882	23,746	15,265
Interest Income Recognized
Impaired loans with no related allowance	40	41	80	89
Impaired loans with related allowance	19	14	38	29
Total Impaired Loans	59	55	118	118
Commercial and industrial loans
Unpaid Principal Balance
Impaired loans with no related allowance	1,048		1,048		828
Impaired loans with related allowance	1,185		1,185
Recorded Investment
Impaired loans with no related allowance	1,012		1,012		806
Impaired loans with related allowance	940		940
Related Allowance	455		455
Average Recorded Investment
Impaired loans with no related allowance	1,013	1,004	1,021	1,006
Impaired loans with related allowance	940	108	940	108
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	679		679		679
Impaired loans with related allowance	2,167		2,167
Recorded Investment
Impaired loans with no related allowance	668		668		679
Impaired loans with related allowance	2,117		2,117
Related Allowance	1,394		1,394
Average Recorded Investment
Impaired loans with no related allowance	668	640	672	640
Impaired loans with related allowance	2,117		2,134
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	7,978		7,978		1,352
Impaired loans with related allowance					7,978
Recorded Investment
Impaired loans with no related allowance	6,909		6,909		614
Impaired loans with related allowance					7,977
Related Allowance					1,429
Average Recorded Investment
Impaired loans with no related allowance	7,314	1,106	7,792	1,167
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	10,160		10,160		11,176
Impaired loans with related allowance	134		134		171
Recorded Investment
Impaired loans with no related allowance	7,381		7,381		8,994
Impaired loans with related allowance	129		129		171
Related Allowance	14		14		6
Average Recorded Investment
Impaired loans with no related allowance	7,998	9,935	8,187	10,241
Impaired loans with related allowance	157		164
Interest Income Recognized
Impaired loans with no related allowance	39	40	78	87
Residential
Unpaid Principal Balance
Impaired loans with no related allowance	117		117		118
Impaired loans with related allowance	1,976		1,976		1,958
Recorded Investment
Impaired loans with no related allowance	99		99		100
Impaired loans with related allowance	1,953		1,953		1,907
Related Allowance	362		362		362
Average Recorded Investment
Impaired loans with no related allowance	38	63	38	63
Impaired loans with related allowance	2,021	1,714	2,029	1,726
Interest Income Recognized
Impaired loans with no related allowance	1	1	2	2
Impaired loans with related allowance	16	12	32	24
Home equity
Unpaid Principal Balance
Impaired loans with no related allowance	49		49		49
Impaired loans with related allowance	366		366		376
Recorded Investment
Impaired loans with no related allowance	49		49		48
Impaired loans with related allowance	349		349		358
Related Allowance	70		70		74
Average Recorded Investment
Impaired loans with no related allowance	49		49
Impaired loans with related allowance	351	302	352	303
Interest Income Recognized
Impaired loans with no related allowance			0
Impaired loans with related allowance	3	2	6	5
Individuals' loans for household and other personal expenditures
Unpaid Principal Balance
Impaired loans with related allowance	14		14		18
Recorded Investment
Impaired loans with related allowance	14		14		18
Related Allowance	1		1		1
Average Recorded Investment
Impaired loans with no related allowance		10		11
Impaired loans with related allowance	14		15
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		353		353
Recorded Investment
Impaired loans with no related allowance	353		353		$ 353
Average Recorded Investment
Impaired loans with no related allowance	$ 353	0	353	0
Interest Income Recognized
Impaired loans with no related allowance		$ 0	$ 0	$ 0