Loans and Allowance for Loan Losses - Additional Information (Detail) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2013 troubled_debt_restructuring		Jun. 30, 2012		Jun. 30, 2013 troubled_debt_restructuring		Jun. 30, 2012		Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred loan fee income	$ 83,000,000				$ 83,000,000				$ 77,000,000
Number of TDRs	19				19
Loans modified in TDRs	34,280,000				34,280,000				34,328,000
Unfunded commitments available for funding	600,000				600,000
Loans modified in TDRs during the period	6,496,000	[1]	13,571,000	[1]	7,153,000	[1]	16,424,000	[1]
Forgiveness Of Principal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in TDRs during the period			10,000,000				10,100,000
Payment Deferrals Granted
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in TDRs during the period	$ 6,500,000		$ 3,600,000		$ 7,200,000		$ 6,300,000

[1] the three and six months ended June 30, 2013. There were partial charge-offs of $10.0 million and $10.9 million, respectively, on loans classified as TDRs during the three and six months ended June 30, 2012.