Loans - Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	$ 14,887,323	$ 13,262,022
Covered loans	129,491	211,891
Total loans	15,016,814	13,473,913
Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	7,457,983	6,562,153
Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,083,193	1,946,896
Covered loans	3,411	5,519
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,399,451	2,237,298
Covered loans	1,167	13,813
Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	6,890,357	6,032,190
Covered loans	70,320	128,691
Construction
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	567,626	529,963
Covered loans	2,027	3,171
Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,946,696	2,515,675
Covered loans	52,566	60,697
Home equity | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	474,730	491,745
Automobile | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	1,219,758	1,144,831
Other consumer | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	388,705	310,320
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	13,539,026	11,752,112
Covered loans	0	0
Total loans	13,539,026	11,752,112
Non-PCI Loans | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	6,531,303	5,529,836
Non-PCI Loans | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	1,991,683	1,843,305
Covered loans	0	0
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,152,638	1,959,927
Covered loans	0	0
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	6,009,760	5,053,742
Covered loans	0	0
Non-PCI Loans | Construction
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	521,543	476,094
Covered loans	0	0
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	2,863,402	2,419,044
Covered loans	0	0
Non-PCI Loans | Home equity | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	392,658	400,136
Non-PCI Loans | Automobile | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	1,219,734	1,144,780
Non-PCI Loans | Other consumer | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	379,291	298,389
PCI Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	1,348,297	1,509,910
Covered loans	129,491	211,891
Total loans	1,477,788	1,721,801
PCI Loans | Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	926,680	1,032,317
PCI Loans | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	91,510	103,591
Covered loans	3,411	5,519
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	246,813	277,371
Covered loans	1,167	13,813
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	880,597	978,448
Covered loans	70,320	128,691
PCI Loans | Construction
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	46,083	53,869
Covered loans	2,027	3,171
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	83,294	96,631
Covered loans	52,566	60,697
PCI Loans | Home equity | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	82,072	91,609
PCI Loans | Automobile
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	24	51
PCI Loans | Other consumer | Consumer loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans	$ 9,414	$ 11,931