Loans - Schedule of Loan Portfolio Non-Covered and Covered PCI Loans and Non-PCI Loans (Detail) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 16,043,107	$ 13,473,913
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		2,540,491	2,251,111
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		8,179,583	6,694,015
Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		7,424,636	6,160,881
Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		754,947	533,134
Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		3,130,541	2,576,372
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		2,192,492	1,952,415
Consumer [Member] | Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		511,203	497,247
Consumer [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		1,239,313	1,144,831
Consumer [Member] | Other consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		441,976	310,337
Non-PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		13,802,636	11,752,112
Non-PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		2,156,549	1,959,927
Non-PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		6,677,226	5,529,836
Non-PCI Loans [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		6,069,532	5,053,742
Non-PCI Loans [Member] | Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		607,694	476,094
Non-PCI Loans [Member] | Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		2,912,079	2,419,044
Non-PCI Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		2,056,782	1,843,305
Non-PCI Loans [Member] | Consumer [Member] | Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		391,809	400,136
Non-PCI Loans [Member] | Consumer [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		1,238,826	1,144,780
Non-PCI Loans [Member] | Consumer [Member] | Other consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		426,147	298,389
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	2,240,471	1,721,801
Covered loans		122,300	211,900
PCI Loans [Member] | Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	383,942	291,184
PCI Loans [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	1,502,357	1,164,179
PCI Loans [Member] | Commercial real estate [Member] | Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	1,355,104	1,107,139
PCI Loans [Member] | Commercial real estate [Member] | Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	147,253	57,040
PCI Loans [Member] | Residential mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	218,462	157,328
PCI Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	135,710	109,110
PCI Loans [Member] | Consumer [Member] | Home equity [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	119,394	97,111
PCI Loans [Member] | Consumer [Member] | Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	487	51
PCI Loans [Member] | Consumer [Member] | Other consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1]	$ 15,829	$ 11,948

[1] PCI loans include covered loans (mostly consisting of commercial real estate and residential mortgage loans) totaling $122.3 million and $211.9 million at December 31, 2015 and 2014, respectively.