Loans - Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable
Loans	$ 22,552,767	$ 18,331,580
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	3,631,597	2,741,425
Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	13,078,736	10,347,882
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	11,706,228	9,496,777
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	1,372,508	851,105
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	3,321,560	2,859,035
Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,520,874	2,383,238
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	549,329	446,280
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,222,721	1,208,902
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	748,824	728,056
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	17,636,934	16,944,365
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	2,736,170	2,549,065
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	9,755,466	9,371,815
Non-PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	8,804,701	8,561,851
Non-PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	950,765	809,964
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	2,817,057	2,717,744
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	2,328,241	2,305,741
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	372,348	373,631
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	1,222,253	1,208,804
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	733,640	723,306
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Loans	4,915,833	1,387,215
Covered loans	33,200	38,700
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Loans	895,427	192,360
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	3,323,270	976,067
PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Loans	2,901,527	934,926
PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable
Loans	421,743	41,141
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Loans	504,503	141,291
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable
Loans	192,633	77,497
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable
Loans	176,981	72,649
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable
Loans	468	98
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable
Loans	$ 15,184	$ 4,750