Loans and Allowance for Loan Losses - Additional Information (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred loan fee income	$ 73,800,000				$ 73,800,000				$ 60,200,000
Loans modified in TDRs	23,487,000				23,487,000				34,275,000
Unfunded commitments available for funding	100,000				100,000
Loans modified in TDRs during the period	1,969,000	[1]	3,429,000	[1]	16,431,000	[1]	11,177,000	[1]
Forgiveness Of Principal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in TDRs during the period					9,600,000
Payment Deferrals Granted
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in TDRs during the period					$ 6,800,000

[1] (1)During the three and nine months ended September 30, 2012, we had partial charge-offs of $1.1 million and $11.0 million, respectively, on loans classified as TDRs. There were $0.6 million partial charge-offs on loans classified as TDRs during the three and nine months ended September 30, 2011.