Allowance for Loan Losses - Aging Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 2,382	$ 4,070
60-89 Days Past Due	1,487	1,305
90 Days or Greater	5,925	8,072
Total Past Due	9,794	13,447
Current	858,184	847,794
Total Loans	867,978	861,241
Past Due 90 Days and Accruing
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	74	105
90 Days or Greater	220	443
Total Past Due	294	548
Current	107,475	115,327
Total Loans	107,769	115,875
Past Due 90 Days and Accruing
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	977	655
60-89 Days Past Due	53	201
90 Days or Greater	1,570	2,098
Total Past Due	2,600	2,954
Current	438,663	440,892
Total Loans	441,263	443,846
Past Due 90 Days and Accruing
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	680	3,140
60-89 Days Past Due	1,405	1,084
90 Days or Greater	4,107	5,531
Total Past Due	6,192	9,755
Current	248,480	240,936
Total Loans	254,672	250,691
Past Due 90 Days and Accruing
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	620
60-89 Days Past Due	8
Total Past Due	628
Current	50,615	39,964
Total Loans	51,243	39,964
Past Due 90 Days and Accruing
Consumer and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	31	170
60-89 Days Past Due	21	20
90 Days or Greater	28
Total Past Due	80	190
Current	12,951	10,675
Total Loans	13,031	10,865
Past Due 90 Days and Accruing