Loans and Leases - Reserve for Loan and Lease Losses Roll Forward (Parenthetical) (Detail) (Commercial Real Estate Loans [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Commercial Real Estate Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Amount of loans charged off prior to being transferred to loans held for sale	$ 1.3