Loans - Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 12,119,086	$ 11,471,447
Covered loans	46,291	96,165
Total loans	12,165,377	11,567,612
Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,803,981	5,410,906
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,802,571	1,565,492
Covered loans	336	799
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,076,512	1,995,084
Covered loans	9,673	26,249
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,346,818	4,981,675
Covered loans	28,937	61,494
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	457,163	429,231
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,436,022	2,499,965
Covered loans	7,345	7,623
Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	435,450	449,009
Automobile [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,091,287	901,399
Other Consumer [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	275,834	215,084
Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	11,535,689	10,761,344
Covered loans	0
Total loans	11,535,689	10,761,344
Non-PCI Loans [Member] | Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,403,131	4,928,797
Non-PCI Loans [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,768,044	1,527,172
Covered loans
Non-PCI Loans [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,941,470	1,820,136
Covered loans
Non-PCI Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	4,961,990	4,521,920
Covered loans
Non-PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	441,141	406,877
Non-PCI Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,423,044	2,485,239
Covered loans
Non-PCI Loans [Member] | Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	401,072	410,875
Non-PCI Loans [Member] | Automobile [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,091,287	901,399
Non-PCI Loans [Member] | Other Consumer [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	275,685	214,898
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	583,397	710,103
Covered loans	46,291	96,165
Total loans	629,688	806,268
PCI Loans [Member] | Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	400,850	482,109
PCI Loans [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	34,527	38,320
Covered loans	336	799
PCI Loans [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	135,042	174,948
Covered loans	9,673	26,249
PCI Loans [Member] | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	384,828	459,755
Covered loans	28,937	61,494
PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	16,022	22,354
PCI Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	12,978	14,726
Covered loans	7,345	7,623
PCI Loans [Member] | Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	34,378	38,134
PCI Loans [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	0	0
PCI Loans [Member] | Other Consumer [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 149	$ 186