Loans - Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Loans	$ 16,135,987	$ 16,043,107
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,537,545	2,540,491
Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Loans	8,361,196	8,179,583
Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	7,585,139	7,424,636
Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	776,057	754,947
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	3,101,814	3,130,541
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,135,432	2,192,492
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	491,555	511,203
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,188,063	1,239,313
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	455,814	441,976
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	14,020,566	13,802,636
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,176,942	2,156,549
Non-PCI Loans | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Loans	6,938,533	6,677,226
Non-PCI Loans | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	6,304,974	6,069,532
Non-PCI Loans | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	633,559	607,694
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	2,892,643	2,912,079
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,012,448	2,056,782
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	380,459	391,809
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,187,742	1,238,826
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	444,247	426,147
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	2,115,421	2,240,471
Covered loans	86,800	122,300
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	360,603	383,942
PCI Loans | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Loans	1,422,663	1,502,357
PCI Loans | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	1,280,165	1,355,104
PCI Loans | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	142,498	147,253
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	209,171	218,462
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	122,984	135,710
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	111,096	119,394
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	321	487
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	$ 11,567	$ 15,829