Loans and Allowance - Summary of Non-Accrual Loans by Loan Class (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 20,421	$ 28,724
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	2,287	3,275
Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	640	1,027
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	764	65
Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	10,406	12,951
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	5,140	9,444
Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	1,126	1,928
Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-accrual loans	$ 58	$ 34