Premises and Equipment (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Depreciation and amortization of premises and equipment, year to date	$ 21.8	$ 21.8	$ 22.2