Loans - Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Loans	$ 18,201,462	$ 17,236,103
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,706,912	2,638,195
Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	10,254,708	9,544,613
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	9,351,068	8,719,667
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	903,640	824,946
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	2,941,435	2,867,918
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,298,407	2,185,377
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	448,842	469,009
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,171,685	1,139,227
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	677,880	577,141
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	16,729,607	15,464,601
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,504,655	2,357,018
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	9,218,515	8,338,594
Non-PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	8,359,833	7,628,328
Non-PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	858,682	710,266
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	2,791,779	2,684,195
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,214,658	2,084,794
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	371,130	376,213
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,171,579	1,139,082
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	671,949	569,499
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	1,471,855	1,771,502
Covered loans	42,600	70,400
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	202,257	281,177
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	1,036,193	1,206,019
PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	991,235	1,091,339
PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	44,958	114,680
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	149,656	183,723
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	83,749	100,583
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	77,712	92,796
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	106	145
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	$ 5,931	$ 7,642