Composition of Loan Portfolio (Parenthetical) (Detail) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 38,359,022	$ 37,356,201
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans	[1]	2,040,574	1,900,445
Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		1,377,964	1,341,216
Lease financing, unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unearned income		65,041	60,278
Non-Covered Loans		662,610	559,229
Specialty Finance Loans | Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		1,500,000	1,300,000
Other Commercial and Industrial Loans | Commercial and Industrial | Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-Covered Loans		$ 500,800	$ 632,900

[1] (1) Includes lease financing receivables, all of which were classified as "pass."