Loans - 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]
Non-covered loans net of unearned discount and deferred loan fees	$ 3,800,000		$ 3,800,000		$ 7,500,000
Non-covered loans	10,941,405,000		10,941,405,000		9,527,797,000
Outstanding contractual principal balances	344,900,000		344,900,000		399,600,000
Loan Portfolio transfer	123,100,000
Sales of loan	0	0	0	0
Non-interest income	390,000	1,600,000	7,500,000	12,000,000
Other non-interest income	7,400,000			7,400,000
Combined loan-to-value, ratio home equity loan	75.00%		75.00%
TDRs not reported as non-accrual loans	109,300,000		109,300,000		101,000,000
Non-performing TDRs	34,600,000		34,600,000		15,500,000
Specific reserves for loan losses			3,300,000	5,400,000
Home Equity Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	18		18
Residential Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans	26		26
Residential Mortgage And Home Equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-performing TDRs	7,400,000		7,400,000
TDR loans performing with contractual terms	3,000,000		3,000,000
Covered By Fdic Loss Share [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-interest income	6,000,000
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,100,000,000		1,100,000,000
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	367,600,000		367,600,000		337,700,000
Commercial and Industrial | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	250,000		250,000
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,441,704,000		1,441,704,000		1,378,728,000
Unsecured loans	78,800,000		78,800,000		66,500,000
Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	$ 8,500,000		$ 8,500,000		$ 9,100,000