Allowance for Loan Losses - Aging Analysis of Past Due Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 4,623	$ 6,111
Current	1,095,956	1,049,139
Total Loans	1,100,817	1,055,506
Past Due 90 Days and Accruing	44	9
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,500	3,145
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	849	1,111
90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,274	1,855
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	259	328
Current	143,362	135,046
Total Loans	143,708	135,462
Commercial and Agriculture [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	249	156
Commercial and Agriculture [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		20
Commercial and Agriculture [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10	152
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,588	1,555
Current	170,674	159,809
Total Loans	172,262	161,364
Commercial Real Estate Owner Occupied [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	334	722
Commercial Real Estate Owner Occupied [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	640	553
Commercial Real Estate Owner Occupied [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	614	280
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	600	463
Current	405,276	395,468
Total Loans	405,876	395,931
Commercial Real Estate Non Owner Occupied [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		147
Commercial Real Estate Non Owner Occupied [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	600	316
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,440	3,368
Current	256,989	243,772
Total Loans	258,580	247,308
Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	263	1,812
Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	198	507
Residential Real Estate [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	979	1,049
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27	27
Current	63,511	56,266
Total Loans	63,538	56,293
Real Estate Construction [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	27	27
Farm Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	504	93
Current	38,565	41,077
Total Loans	39,069	41,170
Farm Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	504	93
Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	205	277
Current	17,579	17,701
Total Loans	17,784	17,978
Past Due 90 Days and Accruing	44	9
Consumer and Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	150	215
Consumer and Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11	31
Consumer and Other [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	44	31
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased Credit-Impaired Loans	238	256
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased Credit-Impaired Loans	87	88
Receivables Acquired with Deteriorated Credit Quality [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased Credit-Impaired Loans	$ 151	$ 168