Allowance for Loan Losses - Aging Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 5,472	$ 4,070
60-89 Days Past Due	1,041	1,305
90 Days or Greater	6,658	8,072
Total Past Due	13,171	13,447
Current	844,197	847,794
Total Loans	857,368	861,241
Past Due 90 Days and Accruing	21
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,292	105
60-89 Days Past Due	230
90 Days or Greater	122	443
Total Past Due	1,644	548
Current	101,721	115,327
Total Loans	103,365	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	1,004	655
60-89 Days Past Due	371	201
90 Days or Greater	1,491	2,098
Total Past Due	2,866	2,954
Current	437,958	440,892
Total Loans	440,824	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	3,114	3,140
60-89 Days Past Due	430	1,084
90 Days or Greater	5,041	5,531
Total Past Due	8,585	9,755
Current	240,707	240,936
Total Loans	249,292	250,691
Past Due 90 Days and Accruing	21
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due
60-89 Days Past Due
90 Days or Greater
Total Past Due
Current	52,788	39,964
Total Loans	52,788	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	62	170
60-89 Days Past Due	10	20
90 Days or Greater	4
Total Past Due	76	190
Current	11,023	10,675
Total Loans	11,099	10,865
Past Due 90 Days and Accruing