Valuation Techniques, Significant Unobservable Inputs, Quantitative Information Non-recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Valuation Technique	Market Approach
Unobservable Input	Discount to reflect realizable value
Loans | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instrument, Fair value	27.7
Loans | Lower Limit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount	15.00%
Loans | Upper Limit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount	30.00%
Other Real Estate Owned
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Valuation Technique	Market Approach
Unobservable Input	Discount to reflect realizable value
Other Real Estate Owned | Fair Value, Inputs, Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instrument, Fair value	1.0
Other Real Estate Owned | Lower Limit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount	15.00%
Other Real Estate Owned | Upper Limit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount	30.00%