Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 10,941,405	$ 9,527,797
Covered loans	207,533	271,844
Total loans	11,148,938	9,799,641
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	4,881,277	3,985,092
Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,441,704	1,378,728
Covered loans	3,012	4,931
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,118,870	1,878,387
Covered loans	51,706	83,742
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	4,445,338	3,574,089
Covered loans	136,304	160,651
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	435,939	411,003
Covered loans	4,751	6,974
Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,499,554	2,285,590
Covered loans	11,760	15,546
Total loans	2,482,363	2,285,590
Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	445,402	469,604
Home Equity | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	492,338	469,604
Automobile Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	789,248	772,490
Other Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans	159,667	136,634
Other Consumer | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	160,118	136,634
Non PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	9,874,585	9,527,797
Covered loans
Total loans	9,874,585	9,527,797
Non PCI Loans | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	4,150,255	3,985,092
Non PCI Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,394,317	1,378,728
Covered loans
Non PCI Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,847,650	1,878,387
Covered loans
Non PCI Loans | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	3,752,963	3,574,089
Covered loans
Non PCI Loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	397,292	411,003
Covered loans
Non PCI Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,482,363	2,285,590
Covered loans
Non PCI Loans | Home Equity | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	445,402	469,604
Non PCI Loans | Automobile Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	789,248	772,490
Non PCI Loans | Other Consumer | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	159,667	136,634
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,066,820
Covered loans	207,533	271,844
Total loans	1,274,353	271,844
PCI Loans | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	731,022
PCI Loans | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	47,387
Covered loans	3,012	4,931
PCI Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	271,220
Covered loans	51,706	83,742
PCI Loans | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	692,375
Covered loans	136,304	160,651
PCI Loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	38,647
Covered loans	4,751	6,974
PCI Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	17,191
Covered loans	11,760	15,546
PCI Loans | Home Equity | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	46,936
PCI Loans | Other Consumer | Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 451