Loans - Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 17,236,103	$ 16,043,107
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,638,195	2,540,491
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	9,544,613	8,179,583
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,719,667	7,424,636
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	824,946	754,947
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,867,918	3,130,541
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,185,377	2,192,492
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	469,009	511,203
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,139,227	1,239,313
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	577,141	441,976
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,464,601	13,802,636
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,357,018	2,156,549
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,338,594	6,677,226
Non-PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	7,628,328	6,069,532
Non-PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	710,266	607,694
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,684,195	2,912,079
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,084,794	2,056,782
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	376,213	391,809
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,139,082	1,238,826
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	569,499	426,147
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,771,502	2,240,471
Covered loans	70,400	122,300
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	281,177	383,942
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,206,019	1,502,357
PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,091,339	1,355,104
PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	114,680	147,253
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	183,723	218,462
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	100,583	135,710
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	92,796	119,394
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	145	487
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 7,642	$ 15,829