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, 2019	Dec. 31, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 24,214,629	$ 23,820,691	$ 22,062,134
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	7,994,191	7,828,538	7,060,871
Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	5,250,953	5,120,096	4,560,880
Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	879,906	948,979	935,358
Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	174,284	144,199	163,470
Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,040,834	1,026,056	977,735
Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	622,884	565,680	414,198
Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	25,330	23,528	9,230
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	6,973,505	6,933,252	6,633,520
Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	803,669	760,824	815,636
Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	147,701	141,481	122,690
Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	926,375	939,322	891,071
Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	964,960	902,248	906,144
Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	895,267	892,478	895,622
Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,117,385	976,560	931,355
Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,007,487	2,205,195	1,955,456
Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	110,661	115,144	115,546
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	528,448	552,343	626,547
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,053,524	1,002,464	869,104
Premium finance receivables | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,988,788	2,841,659	2,576,150
Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	4,389,599	4,373,891	4,002,726
Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	165,770	167,903	187,235
Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	120,804	120,641	105,981
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	24,097,043	23,707,457	21,972,444
Performing | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	7,938,399	7,777,554	7,046,864
Performing | Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	5,212,095	5,085,798	4,550,829
Performing | Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	864,107	932,928	932,957
Performing | Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	174,284	144,199	163,470
Performing | Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,039,699	1,025,421	976,541
Performing | Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	622,884	565,680	413,837
Performing | Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	25,330	23,528	9,230
Performing | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	6,957,572	6,914,123	6,611,695
Performing | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	802,639	759,270	812,497
Performing | Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	147,647	141,374	122,508
Performing | Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	921,893	935,693	890,597
Performing | Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	964,693	901,963	904,717
Performing | Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	887,622	881,725	883,348
Performing | Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,117,082	976,249	931,336
Performing | Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,005,335	2,202,705	1,951,146
Performing | Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	110,661	115,144	115,546
Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	520,563	545,196	616,719
Performing | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,037,615	986,081	851,890
Performing | Premium finance receivables | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,967,433	2,822,525	2,550,261
Performing | Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	4,389,431	4,373,891	4,002,726
Performing | Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	165,770	167,903	187,235
Performing | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	120,260	120,184	105,054
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	117,586	113,234	89,690
Non-performing | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	55,792	50,984	14,007
Non-performing | Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	38,858	34,298	10,051
Non-performing | Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	15,799	16,051	2,401
Non-performing | Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	0	0	0
Non-performing | Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,135	635	1,194
Non-performing | Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	0	0	361
Non-performing | Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	0	0	0
Non-performing | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	15,933	19,129	21,825
Non-performing | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	1,030	1,554	3,139
Non-performing | Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	54	107	182
Non-performing | Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	4,482	3,629	474
Non-performing | Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	267	285	1,427
Non-performing | Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	7,645	10,753	12,274
Non-performing | Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	303	311	19
Non-performing | Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	2,152	2,490	4,310
Non-performing | Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	0	0	0
Non-performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	7,885	7,147	9,828
Non-performing | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	15,909	16,383	17,214
Non-performing | Premium finance receivables | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	21,355	19,134	25,889
Non-performing | Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	168	0	0
Non-performing | Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	0	0	0
Non-performing | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income	$ 544	$ 457	$ 927