Loans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts Notes And Loans Receivable [Line Items]
Outstanding standby letters of credit	$ 474,000	$ 465,000
Outstanding commitments to fund the Overdraft Privilege Program	$ 46,100,000	$ 41,700,000
Evaluation period of net charge-off history	3 years	2 years
Total unpaid principal balance outstanding	$ 27,499,000	$ 32,120,000
Protracted litigation and reserve	546,000
Amounts charged off	$ 3,826,000	4,239,000	$ 8,627,000
Reduction in stated interest rate of loan, minimum outstanding period	6 months
Reduction in stated interest rate of loan, maximum outstanding period	2 years
Allowance for loan losses	$ 17,712,000	17,687,000	21,116,000	$ 21,130,000
Aggregate nonaccrual TDR loans	$ 16,747,000	20,451,000
Troubled debt restructuring period past due considered payment default	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	$ 135,000	193,000	951,000
Amounts charged off	0	73,000	1,800,000
Recorded investment in trouble debt restructuring	26,300,000	31,200,000
Allowance for loan losses	2,300,000	2,600,000
commitment to lend additional amounts	42,000	50,000
Aggregate nonaccrual TDR loans	2,900,000	3,500,000
Aggregate accrual TDR loans	23,400,000	27,700,000
TDRs with Subsequent Default [Member]
Accounts Notes And Loans Receivable [Line Items]
Increment in allowance for loan losses	0	0	0
Amounts charged off	0	$ 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	2.75%
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