Allowance for Loan Losses - Aging Analysis of Past Due Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 5,700	$ 7,053
Current	1,022,922	994,211
Total Loans	1,028,922	1,001,527
Past Due 90 Days and Accruing	12
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	760	4,006
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,073	870
90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,867	2,177
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,249	78
Current	125,181	124,192
Total Loans	126,540	124,402
Commercial and Agriculture [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	111	9
Commercial and Agriculture [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	905	32
Commercial and Agriculture [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	233	37
Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	766	1,302
Current	167,128	166,595
Total Loans	167,894	167,897
Commercial Real Estate Owner Occupied [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	136	982
Commercial Real Estate Owner Occupied [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	248	36
Commercial Real Estate Owner Occupied [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	382	284
Commercial Real Estate Non Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	557	722
Current	369,319	347,717
Total Loans	369,876	348,439
Commercial Real Estate Non Owner Occupied [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	218	269
Commercial Real Estate Non Owner Occupied [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		330
Commercial Real Estate Non Owner Occupied [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	339	123
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,249	4,769
Current	243,502	231,438
Total Loans	245,941	236,338
Residential Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	238	2,640
Residential Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	894	404
Residential Real Estate [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,117	1,725
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		8
Current	56,274	58,890
Total Loans	56,274	58,898
Real Estate Construction [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		8
Farm Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	784
Current	42,505	46,993
Total Loans	43,289	46,993
Farm Real Estate [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	784
Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	95	174
Current	19,013	18,386
Total Loans	19,108	18,560
Past Due 90 Days and Accruing	12
Consumer and Other [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	57	98
Consumer and Other [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	26	68
Consumer and Other [Member] | 90 Days or Greater [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12	8
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased Credit-Impaired Loans	300	263
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased Credit-Impaired Loans	110	132
Receivables Acquired with Deteriorated Credit Quality [Member] | Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Purchased Credit-Impaired Loans	$ 190	$ 131