Loans - Schedule of Loan Assigned Risk Rating within 12 Months of Balance Sheet Date (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	$ 564,729	$ 518,882
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	258,889	257,091
Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	305,840	261,791
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	493,527	460,129
Pass [Member] | Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	230,412	234,835
Pass [Member] | Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	263,115	225,294
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	16,953	18,935
Special Mention [Member] | Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	6,997	6,641
Special Mention [Member] | Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	9,956	12,294
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	51,389	38,960
Substandard [Member] | Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	21,349	15,459
Substandard [Member] | Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	30,040	23,501
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	2,860	858
Doubtful [Member] | Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	131	156
Doubtful [Member] | Commercial Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing receivable recorded investment	$ 2,729	$ 702