Fair Values of Assets and Liabilities - Quantitative Inputs and Assumptions Used in Level 3 Fair Value Measurements (Detail) (USD $) In Thousands, unless otherwise specified			9 Months Ended									9 Months Ended									9 Months Ended								9 Months Ended					9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Prepayment rates [Member]	Sep. 30, 2012 Discount rates [Member]	Sep. 30, 2012 Minimum [Member] Probability of default [Member]	Sep. 30, 2012 Minimum [Member] Prepayment rates [Member]	Sep. 30, 2012 Maximum [Member] Probability of default [Member]	Sep. 30, 2012 Maximum [Member] Prepayment rates [Member]	Sep. 30, 2012 Weighted average [Member] Probability of default [Member]	Sep. 30, 2012 Weighted average [Member] Prepayment rates [Member]	Sep. 30, 2012 Pooled Trust Preferred Collateralized Debt Obligations [Member]	Sep. 30, 2012 Pooled Trust Preferred Collateralized Debt Obligations [Member] Probability of default [Member]	Sep. 30, 2012 Pooled Trust Preferred Collateralized Debt Obligations [Member] Minimum [Member] Discount rates [Member]		Sep. 30, 2012 Pooled Trust Preferred Collateralized Debt Obligations [Member] Maximum [Member] Discount rates [Member]		Sep. 30, 2012 Pooled Trust Preferred Collateralized Debt Obligations [Member] Discounted Cash Flow [Member]	Sep. 30, 2012 Other Investments [Member]	Sep. 30, 2012 Other Investments [Member] Par Value [Member]	Sep. 30, 2012 Interest Rate Swap [Member]	Sep. 30, 2012 Interest Rate Swap [Member] Counterparty credit risk [Member]	Sep. 30, 2012 Interest Rate Swap [Member] Minimum [Member]		Sep. 30, 2012 Interest Rate Swap [Member] Maximum [Member]		Sep. 30, 2012 Interest Rate Swap [Member] Option model [Member]	Sep. 30, 2012 Impaired Loans [Member]		Sep. 30, 2012 Impaired Loans [Member] Discount rates [Member]	Sep. 30, 2012 Impaired Loans [Member] Minimum [Member]	Sep. 30, 2012 Impaired Loans [Member] Maximum [Member]	Sep. 30, 2012 Impaired Loans [Member] Discounted Cash Flow [Member]	Sep. 30, 2012 Other Real Estate Owned [Member]	Sep. 30, 2012 Other Real Estate Owned [Member] Counterparty credit risk [Member]	Sep. 30, 2012 Other Real Estate Owned [Member] Internal Valuation [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Weighted average rate					0.00%	0.00%	100.00%	100.00%	21.73%	13.44%			6.75%	[1]	20.00%	[1]						15.08%	[2]	17.63%	[2]					8.42%	8.83%
Unobservable Inputs			Prepayment rates	Discount rates								Probability of default									Counterparty credit risk								Discount rate
Valuation Technique																	Discounted Cash Flow		Par Value							Option model						Discounted Cash Flow			Internal Valuation
Fair Value	$ 1,181,423	$ 1,212,048									$ 23,051							$ 1,420		$ 0							$ 15,755	[3]					$ 338

[1] incorporates premium related to credit quality and illiquidity of securities.

[2] represents the range of the credit spread curve used in valuation.

[3] the remainder of impaired loans valued using Level 3 inputs are not included in this disclosure as the values of those loans are based on bankruptcy agreement documentation