Loans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts Notes And Loans Receivable [Line Items]
Outstanding standby letters of credit	$ 465,000	$ 62,000
Outstanding commitments to fund the Overdraft Privilege Program	41,700,000	42,000,000
Total unpaid principal balance outstanding	32,120,000	21,284,000
Protracted litigation and reserve	550,000
Amounts charged off	4,239,000	8,627,000	24,268,000
Reduction in stated interest rate of loan, minimum outstanding period	6 months
Reduction in stated interest rate of loan, maximum outstanding period	2 years
Aggregate nonaccrual TDR loans	20,451,000	23,543,000
Aggregate accrual TDR loans		45,000
Maximum period after which troubled debt restructuring is considered to be in payment by default	30 days	30 days
Period of cumulative homogeneous loans past due included in company analysis	90 days
Maximum duration under which loans may be housed under Special Mention category	No Longer Than 12 Months
TDRs [Member]
Accounts Notes And Loans Receivable [Line Items]
Increment in allowance for loan losses	193,000	951,000	584,000
Amounts charged off	73,000	1,800,000	0
Restructured loans	31,200,000	31,500,000
Specific reserve	2,600,000	3,900,000
Aggregate nonaccrual TDR loans	3,500,000	4,900,000
Aggregate accrual TDR loans	27,700,000	26,600,000
TDRs with Subsequent Default [Member]
Accounts Notes And Loans Receivable [Line Items]
Amounts charged off	0	0
Effect of troubled debt restructurings on provision for loan losses	0	0
Secured [Member] | Nonresidential [Member]
Accounts Notes And Loans Receivable [Line Items]
Total unpaid principal balance outstanding	$ 7,000,000
Minimum [Member]
Accounts Notes And Loans Receivable [Line Items]
Interest rate of fixed rate loan	1.99%
Period of maturity of fixed rate loan	3 months
Minimum [Member] | TDRs [Member]
Accounts Notes And Loans Receivable [Line Items]
Extension of the maturity date	6 months
Maximum [Member]
Accounts Notes And Loans Receivable [Line Items]
Interest rate of fixed rate loan	18.00%
Period of maturity of fixed rate loan	30 years
Maximum [Member] | TDRs [Member]
Accounts Notes And Loans Receivable [Line Items]
Extension of the maturity date	10 years