Loans and Allowance for Credit Losses - Loan Portfolio Aging (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	$ 1,478	$ 800
Current	776,239	754,561
Loans	777,717	755,361
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	2,968	2,180
Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	108,585	114,161
Commercial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Current	90,511	88,652
Loans	90,511	88,652
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	372	447
Commercial | Agricultural land and production
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Current	18,074	25,509
Loans	18,074	25,509
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	0	0
Real Estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	579,715	550,796
Real Estate | Owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	87
Current	191,918	191,578
Loans	191,918	191,665
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	0	107
Real Estate | Real estate construction and other land loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	1,397	0
Current	82,738	69,200
Loans	84,135	69,200
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	1,397	0
Real Estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	565
Current	212,008	183,660
Loans	212,008	184,225
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	1,000	1,082
Real Estate | Agricultural real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Current	72,082	86,761
Loans	72,082	86,761
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	0	0
Real Estate | Other real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Current	19,572	18,945
Loans	19,572	18,945
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	0	0
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans	89,417	90,404
Consumer | Equity loans and lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	19	110
Current	61,803	64,384
Loans	61,822	64,494
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	199	526
Consumer | Consumer and installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	62	38
Current	27,533	25,872
Loans	27,595	25,910
Recorded Investment Greater Than 90 Days Accruing	0	0
Non-accrual	0	18
30-59 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	1,476	752
30-59 Days Past Due | Commercial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
30-59 Days Past Due | Commercial | Agricultural land and production
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
30-59 Days Past Due | Real Estate | Owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	87
30-59 Days Past Due | Real Estate | Real estate construction and other land loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	1,397	0
30-59 Days Past Due | Real Estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	565
30-59 Days Past Due | Real Estate | Agricultural real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
30-59 Days Past Due | Real Estate | Other real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
30-59 Days Past Due | Consumer | Equity loans and lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	19	62
30-59 Days Past Due | Consumer | Consumer and installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	60	38
60-89 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	2	48
60-89 Days Past Due | Commercial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
60-89 Days Past Due | Commercial | Agricultural land and production
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
60-89 Days Past Due | Real Estate | Owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
60-89 Days Past Due | Real Estate | Real estate construction and other land loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
60-89 Days Past Due | Real Estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
60-89 Days Past Due | Real Estate | Agricultural real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
60-89 Days Past Due | Real Estate | Other real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
60-89 Days Past Due | Consumer | Equity loans and lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	48
60-89 Days Past Due | Consumer | Consumer and installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	2	0
Greater Than 90 Days Past Due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Commercial | Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Commercial | Agricultural land and production
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Real Estate | Owner occupied
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Real Estate | Real estate construction and other land loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Real Estate | Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Real Estate | Agricultural real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Real Estate | Other real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Consumer | Equity loans and lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	0	0
Greater Than 90 Days Past Due | Consumer | Consumer and installment
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due	$ 0	$ 0