Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of Performance by Loan Class) (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	$ 20,912,781	$ 19,703,172	$ 19,101,261
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,456,034	6,005,422	5,951,544
Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,120,533	3,744,712	3,605,516
Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	853,716	869,721	874,745
Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	194,370	204,225	309,632
Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	896,336	875,070	845,719
Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	381,394	294,914	299,953
Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	9,685	16,780	15,979
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,400,781	6,196,087	5,908,684
Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	673,977	610,239	451,477
Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	102,753	104,801	107,701
Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	880,951	867,674	884,082
Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	836,485	770,601	767,504
Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	934,239	912,593	895,341
Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	864,985	807,624	794,955
Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,974,315	1,952,175	1,851,507
Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	133,076	170,380	156,117
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	672,969	725,793	742,868
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	789,499	705,221	663,598
Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,664,912	2,478,581	2,430,233
Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	3,586,011	3,220,370	3,020,472
Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	209,463	249,657	262,887
Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	133,112	122,041	120,975
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	20,834,798	19,615,718	19,018,133
Performing | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,442,103	5,989,373	5,935,126
Performing | Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,108,252	3,731,097	3,589,707
Performing | Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	853,716	869,721	874,745
Performing | Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	194,370	204,225	309,632
Performing | Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	895,195	873,146	845,485
Performing | Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	380,885	294,404	299,578
Performing | Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	9,685	16,780	15,979
Performing | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,385,903	6,174,163	5,886,059
Performing | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	672,370	607,831	451,077
Performing | Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	102,557	104,407	106,493
Performing | Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	875,803	863,337	880,473
Performing | Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	834,637	763,554	757,537
Performing | Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	932,039	911,996	894,432
Performing | Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	864,416	806,981	794,865
Performing | Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,971,005	1,945,677	1,845,065
Performing | Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	133,076	170,380	156,117
Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	665,388	716,032	733,559
Performing | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	774,756	692,472	651,393
Performing | Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,645,501	2,455,910	2,408,265
Performing | Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	3,579,271	3,216,653	3,020,472
Performing | Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	209,463	249,657	262,887
Performing | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	132,413	121,458	120,372
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	77,983	87,454	83,128
Non-performing | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	13,931	16,049	16,418
Non-performing | Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	12,281	13,615	15,809
Non-performing | Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	0	0	0
Non-performing | Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	0	0	0
Non-performing | Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,141	1,924	234
Non-performing | Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	509	510	375
Non-performing | Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	0	0	0
Non-performing | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	14,878	21,924	22,625
Non-performing | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,607	2,408	400
Non-performing | Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	196	394	1,208
Non-performing | Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	5,148	4,337	3,609
Non-performing | Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,848	7,047	9,967
Non-performing | Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,200	597	909
Non-performing | Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	569	643	90
Non-performing | Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	3,310	6,498	6,442
Non-performing | Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	0	0	0
Non-performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	7,581	9,761	9,309
Non-performing | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	14,743	12,749	12,205
Non-performing | Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	19,411	22,671	21,968
Non-performing | Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,740	3,717	0
Non-performing | Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	0	0	0
Non-performing | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	$ 699	$ 583	$ 603