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
	Mar. 31, 2013	Mar. 31, 2012
Financing Receivable, Modifications [Line Items]
Loans identified during the period	$ 709	$ 10,105
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Loans identified during the period		9,276
Commercial Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Loans identified during the period	235
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		451
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Loans identified during the period	$ 474