Loans and Allowance for Loan Losses - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013 troubled_debt_restructuring		Mar. 31, 2012		Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred loan fee income	$ 77,900,000				$ 77,300,000
Number of TDRs	20
Loans modified in TDRs	33,900,000				34,328,000
Unfunded commitments available for funding	500,000
Loans modified in TDRs during the period	1,375,000	[1]	3,706,000	[1]
Forgiveness Of Principal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in TDRs during the period			600,000
Payment Deferrals Granted
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in TDRs during the period	$ 1,400,000		$ 2,900,000

[1] During the three months ended March 31, 2013, we had no partial charge-offs of loans classified as TDRs. There were partial charge-offs of $0.8 million on loans classified as TDRs during the three months ended March 31, 2012.