Loans and Allowance - Summary of Troubled Debt Restructurings by Modification (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Total Modification	$ 2,717	$ 6,263
Term Modification
Financing Receivable, Modifications [Line Items]
Total Modification	1,295	1,195
Rate Modification
Financing Receivable, Modifications [Line Items]
Total Modification	939	1,215
Combination
Financing Receivable, Modifications [Line Items]
Total Modification	483	3,853
Commercial and industrial loans
Financing Receivable, Modifications [Line Items]
Total Modification	369	397
Commercial and industrial loans | Term Modification
Financing Receivable, Modifications [Line Items]
Total Modification	203
Commercial and industrial loans | Combination
Financing Receivable, Modifications [Line Items]
Total Modification	166	397
Agriculture production financing and other loans to farmers
Financing Receivable, Modifications [Line Items]
Total Modification	387	672
Agriculture production financing and other loans to farmers | Term Modification
Financing Receivable, Modifications [Line Items]
Total Modification	387	660
Agriculture production financing and other loans to farmers | Rate Modification
Financing Receivable, Modifications [Line Items]
Total Modification		12
Commercial and farmland
Financing Receivable, Modifications [Line Items]
Total Modification	996	3,753
Commercial and farmland | Term Modification
Financing Receivable, Modifications [Line Items]
Total Modification	705	297
Commercial and farmland | Rate Modification
Financing Receivable, Modifications [Line Items]
Total Modification	59
Commercial and farmland | Combination
Financing Receivable, Modifications [Line Items]
Total Modification	232	3,456
Residential
Financing Receivable, Modifications [Line Items]
Total Modification	846	1,166
Residential | Term Modification
Financing Receivable, Modifications [Line Items]
Total Modification		238
Residential | Rate Modification
Financing Receivable, Modifications [Line Items]
Total Modification	761	928
Residential | Combination
Financing Receivable, Modifications [Line Items]
Total Modification	85
Home equity
Financing Receivable, Modifications [Line Items]
Total Modification	105	266
Home equity | Term Modification
Financing Receivable, Modifications [Line Items]
Total Modification
Home equity | Rate Modification
Financing Receivable, Modifications [Line Items]
Total Modification	105	266
Home equity | Combination
Financing Receivable, Modifications [Line Items]
Total Modification
Individuals' loans for household and other personal expenditures
Financing Receivable, Modifications [Line Items]
Total Modification	14	9
Individuals' loans for household and other personal expenditures | Term Modification
Financing Receivable, Modifications [Line Items]
Total Modification
Individuals' loans for household and other personal expenditures | Rate Modification
Financing Receivable, Modifications [Line Items]
Total Modification	$ 14	9
Individuals' loans for household and other personal expenditures | Combination
Financing Receivable, Modifications [Line Items]
Total Modification