Loans - Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable
Loans	$ 17,449,498	$ 17,236,103
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,642,319	2,638,195
Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Loans	9,852,272	9,544,613
Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	9,016,418	8,719,667
Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	835,854	824,946
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	2,745,447	2,867,918
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,209,460	2,185,377
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	458,891	469,009
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,150,053	1,139,227
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	600,516	577,141
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	15,794,797	15,464,601
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,398,154	2,357,018
Non-PCI Loans | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Loans	8,709,492	8,338,594
Non-PCI Loans | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	7,951,229	7,628,328
Non-PCI Loans | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	758,263	710,266
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	2,574,346	2,684,195
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,112,805	2,084,794
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	369,232	376,213
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,149,918	1,139,082
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	593,655	569,499
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	1,654,701	1,771,502
Covered loans	47,800	70,400
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	244,165	281,177
PCI Loans | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Loans	1,142,780	1,206,019
PCI Loans | Commercial real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	1,065,189	1,091,339
PCI Loans | Commercial real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	77,591	114,680
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	171,101	183,723
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	96,655	100,583
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	89,659	92,796
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	135	145
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	$ 6,861	$ 7,642