Loans and Allowance for Loan Losses - Schedule of Aging of the Recorded Investment (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financing Receivable Recorded Investment Past Due [Line Items]
Greater Than 90 Days Past Due Still On Accrual		$ 35
Nonaccrual	$ 7,157	8,197
Loans Not Past Due	946,253	950,162
Total Loans	956,070	960,355
Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual	2,570	4,448
Loans Not Past Due	413,912	391,816
Total Loans	417,496	397,017
Commercial and Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual	715	1,182
Loans Not Past Due	233,093	260,684
Total Loans	234,977	262,032
Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Greater Than 90 Days Past Due Still On Accrual		35
Nonaccrual	3,077	2,369
Loans Not Past Due	249,682	247,101
Total Loans	252,919	250,216
Agricultural Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual	447
Loans Not Past Due	15,321	18,042
Total Loans	15,991	18,180
Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual	317	103
Loans Not Past Due	17,482	16,807
Total Loans	17,870	17,103
Agricultural [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Nonaccrual	31	95
Loans Not Past Due	16,763	15,712
Total Loans	16,817	15,807
30 to 59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	1,531	1,047
30 to 59 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	1,007	645
30 to 59 Days Past Due [Member] | Commercial and Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	89	2
30 to 59 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	118	166
30 to 59 Days Past Due [Member] | Agricultural Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	223	138
30 to 59 Days Past Due [Member] | Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	71	96
30 to 59 Days Past Due [Member] | Agricultural [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	23
60 to 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	1,129	914
60 to 89 Days Past Due [Member] | Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	7	108
60 to 89 Days Past Due [Member] | Commercial and Industrial [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	1,080	164
60 to 89 Days Past Due [Member] | Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due	$ 42	545
60 to 89 Days Past Due [Member] | Consumer [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Financing Receivables, Past Due		$ 97