Loans and Allowance - Summary of Non-Accrual Loans by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 28,724	$ 29,998
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	3,275	1,839
Agriculture production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,027	1,329
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	65	73
Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	12,951	15,754
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	9,444	9,523
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,928	1,457
Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 34	$ 23