Loans - Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 13,550,735	$ 13,262,022
Covered loans	183,726	211,891
Total loans	13,734,461	13,473,913
Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	6,635,954	6,562,153
Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,967,012	1,946,896
Covered loans	3,624	5,519
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,361,987	2,237,298
Covered loans	5,940	13,813
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	6,097,017	6,032,190
Covered loans	108,856	128,691
Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	538,937	529,963
Covered loans	3,077	3,171
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,585,782	2,515,675
Covered loans	62,229	60,697
Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	482,265	491,745
Automobile [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,162,963	1,144,831
Other Consumer [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	321,784	310,320
Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	12,085,279	11,752,112
Covered loans	0
Total loans	12,085,279	11,752,112
Non-PCI Loans [Member] | Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,626,271	5,529,836
Non-PCI Loans [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,868,907	1,843,305
Non-PCI Loans [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,094,274	1,959,927
Non-PCI Loans [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	5,142,588	5,053,742
Non-PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	483,683	476,094
Non-PCI Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	2,495,827	2,419,044
Non-PCI Loans [Member] | Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	394,886	400,136
Non-PCI Loans [Member] | Automobile [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,162,919	1,144,780
Non-PCI Loans [Member] | Other Consumer [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	311,102	298,389
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,465,456	1,509,910
Covered loans	183,726	211,891
Total loans	1,649,182	1,721,801
PCI Loans [Member] | Commercial Real Estate Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	1,009,683	1,032,317
PCI Loans [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	98,105	103,591
Covered loans	3,624	5,519
PCI Loans [Member] | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	267,713	277,371
Covered loans	5,940	13,813
PCI Loans [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	954,429	978,448
Covered loans	108,856	128,691
PCI Loans [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	55,254	53,869
Covered loans	3,077	3,171
PCI Loans [Member] | Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	89,955	96,631
Covered loans	62,229	60,697
PCI Loans [Member] | Home Equity [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	87,379	91,609
PCI Loans [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	44	51
PCI Loans [Member] | Other Consumer [Member] | Consumer Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans	$ 10,682	$ 11,931