Loans and Allowance for Loan Losses Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Deferred loan fee income	$ 104,000,000		$ 89,000,000
Loans modified in TDRs	7,151,000		22,433,000
Unfunded commitments available for funding	3,100,000
Loans modified in TDRs during the period	2,738,000	[1]	13,848,000	[1]	28,723,000	[1]
Forgiveness Of Principal [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in TDRs during the period	1,000,000		0		9,000,000
Payment Deferrals Granted
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans modified in TDRs during the period	$ 1,700,000				$ 19,000,000

[1] During 2014 we had no partial charge-offs. In 2013 and 2012 we had partial charge-offs of $11.1 million and $14.3 million respectively, on loans classified as TDRs.