Allowance for Credit Losses (Schedule of Aging of the Company's Loan Portfolio) (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Financing Receivable, Past Due [Line Items]
Nonaccrual	$ 102,930	$ 67,069	$ 83,940
90+ days and still accruing	86,790	7,369	6,101
Loans, net of unearned income	38,167,613	34,789,104	33,264,043
Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Nonaccrual	24,020	0	22,633
90+ days and still accruing	68,067	0	0
Loans, net of unearned income	148,664	30,828	1,520,750
Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	12,259,250	11,904,068	11,187,972
Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	44,293	20,399	26,468
90+ days and still accruing	237	0	0
Loans, net of unearned income	12,215,592	11,345,785	10,105,984
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	43,658	558,283	1,081,988
Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	9,578,184	8,990,286	8,885,714
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	1,525,511	1,356,204	1,343,715
Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Nonaccrual	9,588	20,369	22,676
90+ days and still accruing	0	0	0
Loans, net of unearned income	8,052,673	7,634,082	7,541,999
Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual	1,320	2,574	3,449
90+ days and still accruing	0	0	164
Loans, net of unearned income	328,822	335,155	347,662
Residential real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,235,459	1,637,099	1,547,736
Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	9,787	16,440	0
90+ days and still accruing	0	0	0
Loans, net of unearned income	2,086,795	1,606,271	26,986
Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	13,026	5,433	7,300
90+ days and still accruing	16,624	7,210	5,811
Loans, net of unearned income	5,713,340	4,855,487	4,616,977
Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	1,831	7	0
Loans, net of unearned income	8,004,856	7,042,810	6,655,453
Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	7	477	384
90+ days and still accruing	31	137	126
Loans, net of unearned income	47,702	24,199	22,529
Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	78,910	67,069	83,940
90+ days and still accruing	18,723	7,369	6,101
Loans, net of unearned income	38,018,949	34,758,276	33,237,057
60-89 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	62,400	53,666	32,863
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	489	0	1,540
60-89 days past due | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	23,209	23,492	9,768
60-89 days past due | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,432	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	6,041	284	5,395
60-89 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	125	0	340
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	2,149	982	0
60-89 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	15,301	15,490	10,642
60-89 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	13,628	12,614	5,162
60-89 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	26	34	16
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	61,911	53,666	32,863
30-59 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	132,280	187,423	128,764
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	104	275	1,076
30-59 days past due | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	31,640	42,933	24,086
30-59 days past due | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	3,277	928	1,138
30-59 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	5,715	2,809	12,631
30-59 days past due | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	24,256	37,634	67,187
30-59 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	848	1,120	867
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	15	12,145	0
30-59 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	21,128	22,419	14,614
30-59 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	44,954	66,651	7,040
30-59 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	343	509	125
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	132,176	187,148	128,764
Current
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	37,783,213	34,473,577	33,012,375
Current | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	55,984	30,553	1,495,501
Current | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	12,116,213	11,258,961	10,045,662
Current | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	38,949	556,570	1,080,850
Current | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,518,907	1,352,018	1,330,054
Current | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	8,012,788	7,575,795	7,446,741
Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	326,529	331,461	342,842
Current | Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,074,844	1,576,704	26,986
Current | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	5,647,261	4,804,935	4,578,610
Current | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	7,944,443	6,963,538	6,643,251
Current | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	47,295	23,042	21,878
Current | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	$ 37,727,229	$ 34,443,024	$ 32,985,389