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, 2018	Dec. 31, 2017	Jun. 30, 2017
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	$ 22,610,560	$ 21,640,797	$ 20,743,332
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	7,289,060	6,787,677	6,406,289
Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,621,789	4,342,505	4,094,532
Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	957,339	847,597	838,394
Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	200,060	194,523	234,643
Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,042,755	980,466	871,906
Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	458,614	413,172	356,604
Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	8,503	9,414	10,210
Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,575,084	6,580,618	6,402,494
Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	807,235	745,514	709,587
Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	115,357	126,484	112,153
Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	894,349	894,833	887,684
Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	882,525	883,019	792,791
Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	867,639	951,527	920,494
Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	952,048	915,644	814,598
Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,949,242	1,935,705	2,018,950
Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	106,689	127,892	146,237
Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	593,500	663,045	689,483
Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	895,470	832,120	762,810
Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,833,452	2,634,565	2,648,386
Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,118,666	3,835,790	3,492,709
Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	183,622	199,269	226,334
Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	121,706	107,713	114,827
Performing
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	22,527,278	21,550,635	20,674,282
Performing | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	7,270,672	6,771,981	6,396,098
Performing | Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,608,246	4,331,245	4,085,812
Performing | Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	954,901	845,150	838,394
Performing | Commercial | Mortgage warehouse lines of credit
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	200,060	194,523	234,643
Performing | Commercial | Asset-based lending
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,040,597	978,916	870,970
Performing | Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	458,365	412,733	356,069
Performing | Commercial | PCI - commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	8,503	9,414	10,210
Performing | Commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	6,555,889	6,558,570	6,385,514
Performing | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	805,681	742,371	707,179
Performing | Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	115,129	126,296	111,951
Performing | Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	893,016	892,395	882,878
Performing | Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	882,340	882,208	790,598
Performing | Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	856,099	939,199	918,859
Performing | Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	951,706	915,644	814,244
Performing | Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,945,229	1,932,565	2,013,568
Performing | Commercial real estate | PCI - commercial real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	106,689	127,892	146,237
Performing | Home equity
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	584,404	654,067	680,001
Performing | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	879,645	810,865	748,339
Performing | Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,813,461	2,613,160	2,632,008
Performing | Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,118,666	3,835,790	3,491,663
Performing | Premium finance receivables | PCI - life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	183,622	199,269	226,334
Performing | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	120,919	106,933	114,325
Non-performing
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	83,282	90,162	69,050
Non-performing | Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	18,388	15,696	10,191
Non-performing | Commercial | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	13,543	11,260	8,720
Non-performing | Commercial | Franchise
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	2,438	2,447	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	2,158	1,550	936
Non-performing | Commercial | Leases
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	249	439	535
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	19,195	22,048	16,980
Non-performing | Commercial real estate | Construction
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,554	3,143	2,408
Non-performing | Commercial real estate | Land
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	228	188	202
Non-performing | Commercial real estate | Office
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	1,333	2,438	4,806
Non-performing | Commercial real estate | Industrial
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	185	811	2,193
Non-performing | Commercial real estate | Retail
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	11,540	12,328	1,635
Non-performing | Commercial real estate | Multi-family
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	342	0	354
Non-performing | Commercial real estate | Mixed use and other
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	4,013	3,140	5,382
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	9,096	8,978	9,482
Non-performing | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	15,825	21,255	14,471
Non-performing | Premium finance receivables | Commercial insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	19,991	21,405	16,378
Non-performing | Premium finance receivables | Life insurance loans
Financing Receivable, Recorded Investment [Line Items]
Loans, net of unearned income, excluding covered loans	0	0	1,046
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	$ 787	$ 780	$ 502