Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Unpaid Principal Balance
Impaired loans with no related allowance	$ 23,414		$ 14,555
Impaired loans with related allowance	4,567		10,501
Total Impaired Loans	27,981		25,056
Recorded Investment
Impaired loans with no related allowance	19,415		11,594
Impaired loans with related allowance	4,472		10,431
Total Impaired Loans	23,887		22,025
Related Allowance	1,599		1,872
Average Recorded Investment
Impaired loans with no related allowance	20,149	$ 17,714
Impaired loans with related allowance	4,576	4,598
Total Impaired Loans	24,725	22,312
Interest Income Recognized
Impaired loans with no related allowance	40	54
Impaired loans with related allowance	18	14
Total Impaired Loans	58	68
Commercial and industrial loans
Unpaid Principal Balance
Impaired loans with no related allowance	1,920		828
Recorded Investment
Impaired loans with no related allowance	1,626		806
Average Recorded Investment
Impaired loans with no related allowance	1,641	1,845
Impaired loans with related allowance	0	465
Interest Income Recognized
Impaired loans with no related allowance	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	807		679
Impaired loans with related allowance	2,167
Recorded Investment
Impaired loans with no related allowance	792		679
Impaired loans with related allowance	2,117
Related Allowance	1,172
Average Recorded Investment
Impaired loans with no related allowance	799	640
Impaired loans with related allowance	2,150	0
Interest Income Recognized
Impaired loans with no related allowance	0	0
Impaired loans with related allowance	0	0
Construction
Unpaid Principal Balance
Impaired loans with no related allowance	9,330		1,352
Impaired loans with related allowance			7,978
Recorded Investment
Impaired loans with no related allowance	7,524		614
Impaired loans with related allowance			7,977
Related Allowance			1,429
Average Recorded Investment
Impaired loans with no related allowance	8,270	0
Impaired loans with related allowance	0	1,352
Interest Income Recognized
Impaired loans with no related allowance	0	0
Commercial and farmland
Unpaid Principal Balance
Impaired loans with no related allowance	10,838		11,176
Impaired loans with related allowance	171		171
Recorded Investment
Impaired loans with no related allowance	8,973		8,994
Impaired loans with related allowance	171		171
Related Allowance	6		6
Average Recorded Investment
Impaired loans with no related allowance	8,999	14,450
Impaired loans with related allowance	171	767
Interest Income Recognized
Impaired loans with no related allowance	39	48
Residential
Unpaid Principal Balance
Impaired loans with no related allowance	118		118
Impaired loans with related allowance	1,843		1,958
Recorded Investment
Impaired loans with no related allowance	99		100
Impaired loans with related allowance	1,815		1,907
Related Allowance	348		362
Average Recorded Investment
Impaired loans with no related allowance	38	759
Impaired loans with related allowance	1,884	1,709
Interest Income Recognized
Impaired loans with no related allowance	1	6
Impaired loans with related allowance	15	12
Home equity
Unpaid Principal Balance
Impaired loans with no related allowance	48		49
Impaired loans with related allowance	371		376
Recorded Investment
Impaired loans with no related allowance	48		48
Impaired loans with related allowance	354		358
Related Allowance	72		74
Average Recorded Investment
Impaired loans with no related allowance	48	8
Impaired loans with related allowance	356	305
Interest Income Recognized
Impaired loans with no related allowance		0
Impaired loans with related allowance	3	2
Individuals' loans for household and other personal expenditures
Unpaid Principal Balance
Impaired loans with related allowance	15		18
Recorded Investment
Impaired loans with related allowance	15		18
Related Allowance	1		1
Average Recorded Investment
Impaired loans with no related allowance	1	12
Impaired loans with related allowance	15	0
Interest Income Recognized
Impaired loans with no related allowance		0
Impaired loans with related allowance		0
Public finance and other commercial loans
Unpaid Principal Balance
Impaired loans with no related allowance	353		353
Recorded Investment
Impaired loans with no related allowance	353		$ 353
Average Recorded Investment
Impaired loans with no related allowance	$ 353	0
Interest Income Recognized
Impaired loans with no related allowance		$ 0