Loans - Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 13,262,022	$ 11,471,447
Covered loans	211,891	96,165
Total loans	13,473,913	11,567,612
Commercial real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	6,562,153	5,410,906
Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,946,896	1,565,492
Covered loans	5,519	799
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,237,298	1,995,084
Covered loans	13,813	26,249
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	6,032,190	4,981,675
Covered loans	128,691	61,494
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	529,963	429,231
Covered loans	3,171	0
Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,515,675	2,499,965
Covered loans	60,697	7,623
Home equity [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	491,745	449,009
Automobile [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,144,831	901,399
Other Consumer [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	310,320	215,084
Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	11,752,112	10,761,344
Covered loans	0	0
Total loans	11,752,112	10,761,344
Non-PCI Loans [Member] | Commercial real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,529,836	4,928,797
Non-PCI Loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,843,305	1,527,172
Covered loans	0	0
Non-PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,959,927	1,820,136
Covered loans	0	0
Non-PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,053,742	4,521,920
Covered loans	0	0
Non-PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	476,094	406,877
Covered loans	0	0
Non-PCI Loans [Member] | Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,419,044	2,485,239
Covered loans	0	0
Non-PCI Loans [Member] | Home equity [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	400,136	410,875
Non-PCI Loans [Member] | Automobile [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,144,780	901,399
Non-PCI Loans [Member] | Other Consumer [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	298,389	214,898
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,509,910	710,103
Covered loans	211,891	96,165
Total loans	1,721,801	806,268
PCI Loans [Member] | Commercial real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,032,317	482,109
PCI Loans [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	103,591	38,320
Covered loans	5,519	799
PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	277,371	174,948
Covered loans	13,813	26,249
PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	978,448	459,755
Covered loans	128,691	61,494
PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	53,869	22,354
Covered loans	3,171	0
PCI Loans [Member] | Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	96,631	14,726
Covered loans	60,697	7,623
PCI Loans [Member] | Home equity [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	91,609	38,134
PCI Loans [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans		0
PCI Loans [Member] | Automobile [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	51
PCI Loans [Member] | Other Consumer [Member] | Consumer loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 11,931	$ 186