Loans - Loans Individually Evaluated for Impairment Including Loans Modified in Troubled Debt Restructurings by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance, Total	$ 21,867	$ 19,808
Recorded Investment, Total	19,151	18,308
Allowance for Loan Losses Allocated	2,646	1,882
Commercial, Industrial, and Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance, Related Allowance	4,045	5,929
Recorded Investment, Related Allowance	3,995	4,679
Allowance for Loan Losses Allocated	465	487
Unpaid Principal Balance, No Related Allowance	4,579	2,055
Recorded Investment, No Related Allowance	2,242	2,034
Allowance for Loan Losses Allocated, No Related Allowance	0	0
Commercial Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance, Related Allowance	5,938	5,646
Recorded Investment, Related Allowance	5,609	5,443
Allowance for Loan Losses Allocated	1,977	1,395
Unpaid Principal Balance, No Related Allowance	6,905	6,178
Recorded Investment, No Related Allowance	6,905	6,152
Allowance for Loan Losses Allocated, No Related Allowance	0	0
Residential Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance, Related Allowance	400	0
Recorded Investment, Related Allowance	400	0
Allowance for Loan Losses Allocated	204	0
Unpaid Principal Balance, No Related Allowance	0	0
Recorded Investment, No Related Allowance	0	0
Allowance for Loan Losses Allocated, No Related Allowance	$ 0	$ 0