Allowance for Loan Losses, Allowance for Losses on Lending-Related Commitments and Impaired Loans (Summary of Performance by Loan Class) (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 25,304,659	$ 23,820,691	$ 22,610,560
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	8,270,774	7,828,538	7,289,060
Commercial | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	5,295,775	5,120,096	4,621,789
Commercial | Franchise
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	926,521	948,979	957,339
Commercial | Mortgage warehouse lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	275,170	144,199	200,060
Commercial | Asset-based lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,068,226	1,026,056	1,042,755
Commercial | Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	680,757	565,680	458,614
Commercial | PCI - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	24,325	23,528	8,503
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	7,276,244	6,933,252	6,575,084
Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	838,499	760,824	807,235
Commercial real estate | Land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	145,639	141,481	115,357
Commercial real estate | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	957,218	939,322	894,349
Commercial real estate | Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	956,530	902,248	882,525
Commercial real estate | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	976,201	892,478	867,639
Commercial real estate | Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,240,067	976,560	952,048
Commercial real estate | Mixed use and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	2,035,099	2,205,195	1,949,242
Commercial real estate | PCI - commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	126,991	115,144	106,689
Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	527,370	552,343	593,500
Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,118,178	1,002,464	895,470
Premium finance receivables | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	3,368,423	2,841,659	2,833,452
Premium finance receivables | Life insurance loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	4,487,921	4,373,891	4,118,666
Premium finance receivables | PCI - life insurance loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	146,557	167,903	183,622
Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	109,192	120,641	121,706
Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	25,191,212	23,707,457	22,527,278
Performing | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	8,222,682	7,777,554	7,270,672
Performing | Commercial | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	5,259,385	5,085,798	4,608,246
Performing | Commercial | Franchise
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	915,445	932,928	954,901
Performing | Commercial | Mortgage warehouse lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	275,170	144,199	200,060
Performing | Commercial | Asset-based lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,067,658	1,025,421	1,040,597
Performing | Commercial | Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	680,699	565,680	458,365
Performing | Commercial | PCI - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	24,325	23,528	8,503
Performing | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	7,255,369	6,914,123	6,555,889
Performing | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	837,469	759,270	805,681
Performing | Commercial real estate | Land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	144,413	141,374	115,129
Performing | Commercial real estate | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	948,237	935,693	893,016
Performing | Commercial real estate | Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	956,162	901,963	882,340
Performing | Commercial real estate | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	969,334	881,725	856,099
Performing | Commercial real estate | Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,239,771	976,249	951,706
Performing | Commercial real estate | Mixed use and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	2,032,992	2,202,705	1,945,229
Performing | Commercial real estate | PCI - commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	126,991	115,144	106,689
Performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	518,881	545,196	584,404
Performing | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,103,942	986,081	879,645
Performing | Premium finance receivables | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	3,347,650	2,822,525	2,813,461
Performing | Premium finance receivables | Life insurance loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	4,487,331	4,373,891	4,118,666
Performing | Premium finance receivables | PCI - life insurance loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	146,557	167,903	183,622
Performing | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	108,800	120,184	120,919
Non-performing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	113,447	113,234	83,282
Non-performing | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	48,092	50,984	18,388
Non-performing | Commercial | Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	36,390	34,298	13,543
Non-performing | Commercial | Franchise
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	11,076	16,051	2,438
Non-performing | Commercial | Mortgage warehouse lines of credit
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	0	0	0
Non-performing | Commercial | Asset-based lending
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	568	635	2,158
Non-performing | Commercial | Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	58	0	249
Non-performing | Commercial | PCI - commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	0	0	0
Non-performing | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	20,875	19,129	19,195
Non-performing | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,030	1,554	1,554
Non-performing | Commercial real estate | Land
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,226	107	228
Non-performing | Commercial real estate | Office
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	8,981	3,629	1,333
Non-performing | Commercial real estate | Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	368	285	185
Non-performing | Commercial real estate | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	6,867	10,753	11,540
Non-performing | Commercial real estate | Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	296	311	342
Non-performing | Commercial real estate | Mixed use and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	2,107	2,490	4,013
Non-performing | Commercial real estate | PCI - commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	0	0	0
Non-performing | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	8,489	7,147	9,096
Non-performing | Residential real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	14,236	16,383	15,825
Non-performing | Premium finance receivables | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	20,773	19,134	19,991
Non-performing | Premium finance receivables | Life insurance loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	590	0	0
Non-performing | Premium finance receivables | PCI - life insurance loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	0	0	0
Non-performing | Consumer and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 392	$ 457	$ 787