Allowance For Loan Losses and Credit Quality Information (Schedule of Loans Identified as Troubled Debt Restructurings During Periods Indicated (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012
Financing Receivable, Modifications [Line Items]
Loans identified during the period	$ 5,654	$ 16,846
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Loans identified during the period	710	9,986
Construction [Member]
Financing Receivable, Modifications [Line Items]
Loans identified during the period		378
Residential [Member]
Financing Receivable, Modifications [Line Items]
Loans identified during the period	2,779	4,170
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Loans identified during the period	$ 2,165	$ 2,312