Loans and Allowance for Loan and Lease Losses - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015 RiskGrades SecurityLoan Methodologies	Mar. 31, 2014 SecurityLoan	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Period used to calculate required all without specific reserve	36 months
Number of methodologies	3
Number of years taken into account for borrower's historic cash flows for grade one	5 years
Borrower rating, grade nine doubtful	9
Borrower rating, grade eight substandard	8
Period of loan transferred to non-accrual	90 days
Troubled debt restructurings part of non-accrual loans	$ 1,172,000		$ 1,082,000
Number of TDR loans	0	0
Number of days for delay in payment	90 days
Periods of restructuring loans past due	12 months
Number of troubled debt restructured loans with default payment	0	0
Maximum [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Amount of Charge-offs to be approved by Chief Credit Officer	100,000
Minimum [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Amount of forgiveness of debt required to be approved by Loan Committee	100,000
Amount of Charge-offs to be approved by Chief Credit Officer	$ 10,000