Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	$ 55,948	$ 64,215
Total Losses	(6,614)	(6,351)
Impaired Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	46,657	59,784
Total Losses	(6,008)	(5,565)
Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	9,291	4,431
Total Losses	(606)	(786)
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	55,948	64,215
Fair Value, Inputs, Level 3 | Impaired Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	46,657	59,784
Fair Value, Inputs, Level 3 | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	$ 9,291	$ 4,431