Loans and Leases and the Allowance for Credit Losses - Summary of Loan grades applied various classes of Commercial and Real Estate Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 93,582,894	$ 98,535,867
Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	14,856,175	16,963,561
Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,233,297	1,387,378
Commercial, Financial, Leasing, etc. [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,514,940	27,574,564
Commercial, Financial, Leasing, etc. [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	21,091,726	25,927,474
Commercial, Financial, Leasing, etc. [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,143,025	1,340,263
Commercial, Financial, Leasing, etc. [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	280,189	306,827
Commercial, Financial, Leasing, etc. [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	10,216,664	12,063,060
Commercial, Financial, Leasing, etc. [Member] | Revolving Loans [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	9,725,075	11,352,416
Commercial, Financial, Leasing, etc. [Member] | Revolving Loans [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	393,348	584,751
Commercial, Financial, Leasing, etc. [Member] | Revolving Loans [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	98,241	125,893
Commercial, Financial, Leasing, etc. [Member] | Revolving Loans Converted to Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	38,237	42,974
Commercial, Financial, Leasing, etc. [Member] | Revolving Loans Converted to Term Loans [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	16,195	21,286
Commercial, Financial, Leasing, etc. [Member] | Revolving Loans Converted to Term Loans [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	14,373	13,970
Commercial, Financial, Leasing, etc. [Member] | Revolving Loans Converted to Term Loans [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	7,669	7,718
Commercial [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	26,985,800	27,680,340
Commercial [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,843,486	23,282,787
Commercial [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	4,989,444	3,621,659
Commercial [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,152,870	775,894
Commercial [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	816,750	954,022
Commercial [Member] | Revolving Loans [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	729,377	875,348
Commercial [Member] | Revolving Loans [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	50,191	44,260
Commercial [Member] | Revolving Loans [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	37,182	34,414
Residential Builder and Developer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,356,323	1,249,738
Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,214,925	1,113,915
Residential Builder and Developer [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	140,804	134,729
Residential Builder and Developer [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	594	1,094
Residential Builder and Developer [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	245,237	240,993
Residential Builder and Developer [Member] | Revolving Loans [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	243,749	236,943
Residential Builder and Developer [Member] | Revolving Loans [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,488	4,050
Other Commercial Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	8,681,829	8,707,811
Other Commercial Construction [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	6,748,997	7,644,349
Other Commercial Construction [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,774,133	949,423
Other Commercial Construction [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	158,699	114,039
Other Commercial Construction [Member] | Revolving Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	42,662	80,018
Other Commercial Construction [Member] | Revolving Loans [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	38,391	74,611
Other Commercial Construction [Member] | Revolving Loans [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	4,271	5,407
Term Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	14,325,317	20,949,019	$ 13,515,748	$ 15,628,942	$ 13,584,252	$ 10,466,749	$ 8,778,600	$ 7,893,838	$ 6,419,053	$ 6,013,013
Term Loans [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	4,183,196	8,128,774	2,470,195	2,388,900	1,835,319	1,675,653	1,294,396	989,229	659,030	779,407
Term Loans [Member] | Commercial, Financial, Leasing, etc. [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	3,966,960	7,732,728	2,312,034	2,277,233	1,700,134	1,505,486	1,149,584	930,834	586,185	719,796
Term Loans [Member] | Commercial, Financial, Leasing, etc. [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	210,621	388,326	137,816	84,358	105,118	113,940	91,922	41,587	47,157	39,930
Term Loans [Member] | Commercial, Financial, Leasing, etc. [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	5,615	7,720	20,345	27,309	30,067	56,227	52,890	16,808	25,688	19,681
Term Loans [Member] | Commercial [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,310,876	3,906,363	3,529,419	5,203,887	4,967,878	3,925,746	3,855,790	3,018,239	2,859,317	3,511,628
Term Loans [Member] | Commercial [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,259,468	3,353,450	2,835,919	4,681,834	4,069,520	3,299,095	2,765,720	2,628,061	2,176,210	2,746,165
Term Loans [Member] | Commercial [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	22,831	526,037	553,477	400,154	661,516	579,507	1,042,329	290,885	566,644	568,144
Term Loans [Member] | Commercial [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	28,577	26,876	140,023	121,899	236,842	47,144	47,741	99,293	116,463	197,319
Term Loans [Member] | Residential Builder and Developer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	650,062	509,985	170,139	331,245	214,285	124,289	58,587	18,469	6,203	10,976
Term Loans [Member] | Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	647,863	506,295	166,832	223,880	94,758	109,453	44,419	15,048	5,573	10,976
Term Loans [Member] | Residential Builder and Developer [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,199	3,690	3,307	106,847	119,009	14,836	14,168	3,421	630
Term Loans [Member] | Residential Builder and Developer [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount				518	518
Term Loans [Member] | Other Commercial Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	661,723	1,087,785	1,860,331	3,213,005	3,119,174	2,442,676	1,844,378	1,175,501	603,178	389,889
Term Loans [Member] | Other Commercial Construction [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	661,068	1,050,258	1,817,753	2,998,921	2,445,555	2,048,063	1,108,676	945,339	270,054	233,127
Term Loans [Member] | Other Commercial Construction [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	655	37,192	$ 42,578	148,492	589,790	381,091	700,577	225,949	320,718	144,665
Term Loans [Member] | Other Commercial Construction [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount		335		$ 65,592	$ 83,829	$ 13,522	$ 35,125	$ 4,213	$ 12,406	$ 12,097
Term Loans Prior Period [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	20,870,452	19,233,367
Term Loans Prior Period [Member] | Commercial, Financial, Leasing, etc. [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,817,903	1,506,567
Term Loans Prior Period [Member] | Commercial, Financial, Leasing, etc. [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	1,635,559	1,387,695
Term Loans Prior Period [Member] | Commercial, Financial, Leasing, etc. [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	142,670	73,401
Term Loans Prior Period [Member] | Commercial, Financial, Leasing, etc. [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	39,674	45,471
Term Loans Prior Period [Member] | Commercial [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	8,645,770	7,160,455
Term Loans Prior Period [Member] | Commercial [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	6,007,272	5,698,834
Term Loans Prior Period [Member] | Commercial [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	2,092,456	1,212,672
Term Loans Prior Period [Member] | Commercial [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	546,042	248,949
Term Loans Prior Period [Member] | Residential Builder and Developer [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	11,810	13,781
Term Loans Prior Period [Member] | Residential Builder and Developer [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	11,731	11,320
Term Loans Prior Period [Member] | Residential Builder and Developer [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	3	1,885
Term Loans Prior Period [Member] | Residential Builder and Developer [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	76	576
Term Loans Prior Period [Member] | Other Commercial Construction [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	550,383	318,937
Term Loans Prior Period [Member] | Other Commercial Construction [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	407,500	294,030
Term Loans Prior Period [Member] | Other Commercial Construction [Member] | Criticized Accrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	119,815	12,034
Term Loans Prior Period [Member] | Other Commercial Construction [Member] | Criticized Nonaccrual [Member]
Financing Receivable Recorded Investment [Line Items]
Loans and leases, net of unearned discount	$ 23,068	$ 12,873