Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	$ 49,550	$ 64,215
Total Losses	(6,918)	(6,351)
Impaired Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	43,624	59,784
Total Losses	(6,730)	(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	5,926	4,431
Total Losses	(188)	(786)
Quoted Prices in Active Markets for Identical Assets (Level 1) | Impaired Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	0	0
Total Losses	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	0	0
Total Losses	0	0
Significant Other Observable Inputs (Level 2) | Impaired Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	0	0
Total Losses	0	0
Significant Other Observable Inputs (Level 2) | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	0	0
Total Losses	0	0
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value adjustments (impairment) on nonrecurring basis	49,550	64,215
Total Losses	0	0
Significant Unobservable 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	43,624	59,784
Total Losses	0	0
Significant Unobservable 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	5,926	4,431
Total Losses	$ 0	$ 0