Loans - Loan Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	$ 1,141,992	$ 1,055,506
Allowance for loan losses	(12,946)	(13,305)
Net loans	1,129,046	1,042,201
Commercial and Agriculture [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	147,537	135,462
Commercial Real Estate Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	167,678	161,364
Commercial Real Estate Non Owner Occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	424,430	395,931
Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	267,839	247,308
Real Estate Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	77,978	56,293
Farm Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	38,966	41,170
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans	$ 17,564	$ 17,978