Allowance for Loan Losses - Aging Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 1,064	$ 4,044
60-89 Days Past Due	1,058	1,839
90 Days or Greater	8,670	16,319
Total Past Due	10,792	22,202
Current	808,779	793,351
Total Loans	819,571	815,553
Past Due 90 Days and Accruing		80
Commercial and Agriculture [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due		31
60-89 Days Past Due	4	72
90 Days or Greater	304	553
Total Past Due	308	656
Current	105,522	100,005
Total Loans	105,830	100,661
Past Due 90 Days and Accruing
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	271	1,000
60-89 Days Past Due	653	533
90 Days or Greater	2,929	6,794
Total Past Due	3,853	8,327
Current	427,880	426,481
Total Loans	431,733	434,808
Past Due 90 Days and Accruing		80
Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	733	2,843
60-89 Days Past Due	393	1,214
90 Days or Greater	5,412	8,527
Total Past Due	6,538	12,584
Current	237,855	238,014
Total Loans	244,393	250,598
Past Due 90 Days and Accruing
Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due		43
60-89 Days Past Due
90 Days or Greater		416
Total Past Due		459
Current	26,661	19,218
Total Loans	26,661	19,677
Past Due 90 Days and Accruing
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	60	127
60-89 Days Past Due	8	20
90 Days or Greater	25	29
Total Past Due	93	176
Current	10,861	9,633
Total Loans	10,954	9,809
Past Due 90 Days and Accruing