Loans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 D	Dec. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans net of unearned discounts and deferred loan fees	$ 3,400,000	$ 7,500,000
Non-covered loans	10,842,125,000	9,527,797,000
Outstanding contractual principal balances	0	399,600,000
Loan portfolio transfer	124,300,000
Sales of loans	0	0
Non-interest income	(7,500,000)	13,400,000	6,300,000
Combined loan-to-value ratio home equity loan	75.00%
Accrued interest on non-accrual loans	7,200,000	6,900,000	7,900,000
Interest income recognized and classified as non-accrual	590,000	1,600,000
Interest on impaired loans	194,000	1,100,000
Average balance of impaired loans			104,100,000
TDRs not reported as non-accrual loans	105,400,000	101,000,000
Non-performing TDRs	41,800,000	15,500,000
Specific reserves for loan losses	15,000,000	9,000,000
Number of days loans placed on non-accrual status	90
Covered By Fdic Loss Share [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-interest income	(5,500,000)
Residential loans and home equity loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-performing TDRs	6,400,000
TDRs loans performing with contractual terms	3,400,000
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,100,000,000	321,900,000,000
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,451,717,000	1,378,728,000
Unsecured loans	126,800,000	66,500,000
Credit card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	8,600,000	9,100,000
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	307,000,000	337,700,000
Commercial and industrial [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans	$ 250,000