Allowance for Credit Losses (Schedule of Aging of the Company's Loan Portfolio) (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Financing Receivable, Past Due [Line Items]
Nonaccrual	$ 89,694	$ 67,069	$ 82,698
90+ days and still accruing	56,786	7,369	4,992
Loans, net of unearned income	37,053,103	34,789,104	32,911,187
Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Nonaccrual	23,815	0	0
90+ days and still accruing	50,314	0	0
Loans, net of unearned income	113,856	30,828	50,778
Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	12,047,105	11,904,068	11,442,276
Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	32,436	20,399	23,232
90+ days and still accruing	0	0	1,244
Loans, net of unearned income	11,965,016	11,345,785	9,562,869
Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	0	15	0
Loans, net of unearned income	82,089	558,283	1,879,407
Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	9,407,205	8,990,286	8,678,369
Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Nonaccrual	889	1,377	1,030
90+ days and still accruing	0	0	0
Loans, net of unearned income	1,506,318	1,356,204	1,385,249
Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Nonaccrual	9,829	20,369	25,005
90+ days and still accruing	0	0	0
Loans, net of unearned income	7,900,887	7,634,082	7,293,120
Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual	1,084	2,574	3,478
90+ days and still accruing	0	0	0
Loans, net of unearned income	325,826	335,155	369,806
Residential real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,078,907	1,637,099	1,530,285
Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	8,330	16,440	23,050
90+ days and still accruing	0	0	0
Loans, net of unearned income	1,965,051	1,606,271	1,479,507
Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	13,303	5,433	6,418
90+ days and still accruing	6,447	7,210	3,570
Loans, net of unearned income	5,541,447	4,855,487	4,521,871
Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	0	7	0
Loans, net of unearned income	7,608,433	7,042,810	6,359,556
Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	8	477	485
90+ days and still accruing	25	137	178
Loans, net of unearned income	44,180	24,199	9,024
Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	65,879	67,069	82,698
90+ days and still accruing	6,472	7,369	4,992
Loans, net of unearned income	36,939,247	34,758,276	32,860,409
60-89 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	41,623	53,666	19,252
60-89 days past due | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	272	0	0
60-89 days past due | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	7,756	23,492	5,204
60-89 days past due | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	9,033	770	0
60-89 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	0	0	0
60-89 days past due | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	6,771	284	4,382
60-89 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	154	0	301
60-89 days past due | Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	534	982	1,584
60-89 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	15,299	15,490	7,759
60-89 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,796	12,614	0
60-89 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	8	34	22
60-89 days past due | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	41,351	53,666	19,252
30-59 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	138,004	187,423	73,925
30-59 days past due | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	0	275	0
30-59 days past due | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	13,897	42,933	18,468
30-59 days past due | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	223	928	10
30-59 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,144	2,809	2,207
30-59 days past due | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	33,076	37,634	17,491
30-59 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	930	1,120	777
30-59 days past due | Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	147	12,145	2,139
30-59 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	23,313	22,419	8,793
30-59 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	65,155	66,651	23,965
30-59 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	119	509	75
30-59 days past due | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	138,004	187,148	73,925
Current
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	36,726,996	34,473,577	32,730,320
Current | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	39,455	30,553	50,778
Current | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	11,910,927	11,258,961	9,514,721
Current | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	72,833	556,570	1,879,397
Current | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,504,285	1,352,018	1,382,012
Current | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	7,851,211	7,575,795	7,246,242
Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	323,658	331,461	365,250
Current | Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,956,040	1,576,704	1,452,734
Current | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	5,483,085	4,804,935	4,495,331
Current | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	7,541,482	6,963,538	6,335,591
Current | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	44,020	23,042	8,264
Current | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	$ 36,687,541	$ 34,443,024	$ 32,679,542