Loans - Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	$ 14,335,063	$ 13,262,022
Covered loans	145,231	211,891
Total loans	14,480,294	13,473,913
Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	7,283,964	6,562,153
Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,031,613	1,946,896
Covered loans	3,352	5,519
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,370,794	2,237,298
Covered loans	1,237	13,813
Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	6,700,426	6,032,190
Covered loans	82,723	128,691
Construction
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	583,538	529,963
Covered loans	2,530	3,171
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,648,692	2,515,675
Covered loans	55,389	60,697
Home equity | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	479,027	491,745
Automobile | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	1,198,064	1,144,831
Other consumer | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	354,522	310,320
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	12,908,822	11,752,112
Covered loans	0	0
Total loans	12,908,822	11,752,112
Non-PCI Loans | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	6,305,094	5,529,836
Non-PCI Loans | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	1,933,565	1,843,305
Covered loans	0	0
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,111,032	1,959,927
Covered loans	0	0
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	5,771,813	5,053,742
Covered loans	0	0
Non-PCI Loans | Construction
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	533,281	476,094
Covered loans	0	0
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,559,131	2,419,044
Covered loans	0	0
Non-PCI Loans | Home equity | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	391,793	400,136
Non-PCI Loans | Automobile | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	1,198,035	1,144,780
Non-PCI Loans | Other consumer | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	343,737	298,389
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	1,426,241	1,509,910
Covered loans	145,231	211,891
Total loans	1,571,472	1,721,801
PCI Loans | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	978,870	1,032,317
PCI Loans | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	98,048	103,591
Covered loans	3,352	5,519
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	259,762	277,371
Covered loans	1,237	13,813
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	928,613	978,448
Covered loans	82,723	128,691
PCI Loans | Construction
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	50,257	53,869
Covered loans	2,530	3,171
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	89,561	96,631
Covered loans	55,389	60,697
PCI Loans | Home equity | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	87,234	91,609
PCI Loans | Automobile
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	29	51
PCI Loans | Other consumer | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	$ 10,785	$ 11,931