Loans and Allowance for Loan and Lease Losses - Loan Portfolio Aging Analysis (Parenthetical) (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans classified as nonaccrual that are less than 30 days past due	$ 992,000	$ 667,000
Residential Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans classified as nonaccrual that are less than 30 days past due	613,000	587,000
Commercial Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans classified as nonaccrual that are less than 30 days past due	$ 379,000	$ 80,000