Loans - Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Loans	$ 17,710,760	$ 17,236,103
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,631,312	2,638,195
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable
Loans	10,111,587	9,544,613
Commercial Real Estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	9,230,514	8,719,667
Commercial Real Estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	881,073	824,946
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	2,724,777	2,867,918
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,243,084	2,185,377
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	450,510	469,009
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,150,343	1,139,227
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	642,231	577,141
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	16,169,291	15,464,601
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,417,924	2,357,018
Non-PCI Loans | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable
Loans	9,026,431	8,338,594
Non-PCI Loans | Commercial Real Estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	8,201,235	7,628,328
Non-PCI Loans | Commercial Real Estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	825,196	710,266
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	2,569,500	2,684,195
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,155,436	2,084,794
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	369,372	376,213
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,150,217	1,139,082
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	635,847	569,499
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	1,541,469	1,771,502
Covered loans	44,500	70,400
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	213,388	281,177
PCI Loans | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable
Loans	1,085,156	1,206,019
PCI Loans | Commercial Real Estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	1,029,279	1,091,339
PCI Loans | Commercial Real Estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	55,877	114,680
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	155,277	183,723
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	87,648	100,583
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	81,138	92,796
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	126	145
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	$ 6,384	$ 7,642