Loans and Allowance - Summary of Troubled Debt Restructurings (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 3,004	$ 7,165
Post-Modification Recorded Balance	$ 2,902	$ 7,035
Number of Loans | loan	34	37
Commercial and industrial loans
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 599	$ 410
Post-Modification Recorded Balance	$ 376	$ 410
Number of Loans | loan	3	4
Agriculture production financing and other loans to farmers
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 387	$ 1,368
Post-Modification Recorded Balance	$ 387	$ 1,234
Number of Loans | loan	3	4
Commercial and farmland
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 1,022	$ 3,978
Post-Modification Recorded Balance	$ 1,156	$ 3,954
Number of Loans | loan	8	7
Residential
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 788	$ 1,126
Post-Modification Recorded Balance	$ 862	$ 1,183
Number of Loans | loan	15	17
Home equity
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 195	$ 266
Post-Modification Recorded Balance	$ 107	$ 244
Number of Loans | loan	4	4
Individuals' loans for household and other personal expenditures
Financing Receivable, Modifications [Line Items]
Pre-Modification Recorded Balance	$ 13	$ 17
Post-Modification Recorded Balance	$ 14	$ 10
Number of Loans | loan	1	1