Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of Performance by Loan Class) (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	$ 22,062,134	$ 21,640,797	$ 19,931,058
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	7,060,871	6,787,677	6,081,489
Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,560,880	4,342,505	3,891,075
Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	935,358	847,597	823,734
Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	163,470	194,523	154,180
Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	977,735	980,466	881,004
Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	414,198	413,172	320,010
Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	9,230	9,414	11,486
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,633,520	6,580,618	6,261,682
Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	815,636	745,514	655,333
Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	122,690	126,484	105,079
Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	891,071	894,833	870,666
Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	906,144	883,019	792,962
Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	895,622	951,527	911,786
Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	931,355	915,644	804,776
Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,955,456	1,935,705	1,963,744
Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	115,546	127,892	157,336
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	626,547	663,045	708,258
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	869,104	832,120	720,608
Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,576,150	2,634,565	2,446,946
Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,002,726	3,835,790	3,352,857
Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	187,235	199,269	240,706
Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	105,981	107,713	118,512
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	21,972,444	21,550,635	19,852,079
Performing | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	7,046,864	6,771,981	6,067,082
Performing | Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,550,829	4,331,245	3,878,939
Performing | Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	932,957	845,150	823,411
Performing | Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	163,470	194,523	154,180
Performing | Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	976,541	978,916	879,626
Performing | Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	413,837	412,733	319,440
Performing | Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	9,230	9,414	11,486
Performing | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,611,695	6,558,570	6,240,873
Performing | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	812,497	742,371	652,925
Performing | Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	122,508	126,296	104,729
Performing | Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	890,597	892,395	867,153
Performing | Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	904,717	882,208	785,958
Performing | Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	883,348	939,199	911,197
Performing | Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	931,336	915,644	804,108
Performing | Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,951,146	1,932,565	1,957,467
Performing | Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	115,546	127,892	157,336
Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	616,719	654,067	696,536
Performing | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	851,890	810,865	708,665
Performing | Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,550,261	2,613,160	2,429,326
Performing | Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,002,726	3,835,790	3,350,833
Performing | Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	187,235	199,269	240,706
Performing | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	105,054	106,933	118,058
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	89,690	90,162	78,979
Non-performing | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	14,007	15,696	14,407
Non-performing | Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	10,051	11,260	12,136
Non-performing | Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,401	2,447	323
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	1,194	1,550	1,378
Non-performing | Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	361	439	570
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	21,825	22,048	20,809
Non-performing | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	3,139	3,143	2,408
Non-performing | Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	182	188	350
Non-performing | Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	474	2,438	3,513
Non-performing | Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,427	811	7,004
Non-performing | Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	12,274	12,328	589
Non-performing | Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	19	0	668
Non-performing | Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,310	3,140	6,277
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	9,828	8,978	11,722
Non-performing | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	17,214	21,255	11,943
Non-performing | Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	25,889	21,405	17,620
Non-performing | Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	0	0	2,024
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	$ 927	$ 780	$ 454