Allowance for Credit Losses (Schedule of Aging of the Company's Loan Portfolio) (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Financing Receivable, Past Due [Line Items]
Nonaccrual	$ 49,560	$ 67,069	$ 94,115
90+ days and still accruing	41,364	7,369	4,944
Loans, net of unearned income	35,280,547	34,789,104	33,171,233
Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Nonaccrual	4,661	0	0
90+ days and still accruing	28,958	0	0
Loans, net of unearned income	50,096	30,828	51,841
Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	11,583,963	11,904,068	12,708,207
Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	16,878	20,399	22,459
90+ days and still accruing	0	0	0
Loans, net of unearned income	11,329,999	11,345,785	9,415,225
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	253,964	558,283	3,292,982
Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	9,235,074	8,990,286	8,544,779
Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Nonaccrual	1,054	1,377	2,673
90+ days and still accruing	0	0	0
Loans, net of unearned income	1,396,406	1,356,204	1,353,324
Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Nonaccrual	11,247	20,369	31,707
90+ days and still accruing	0	0	0
Loans, net of unearned income	7,838,668	7,634,082	7,191,455
Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual	1,747	2,574	5,536
90+ days and still accruing	0	0	0
Loans, net of unearned income	321,435	335,155	390,253
Residential real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,799,985	1,637,099	1,421,973
Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	7,262	16,440	21,553
90+ days and still accruing	0	0	0
Loans, net of unearned income	1,749,889	1,606,271	1,370,132
Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	6,707	5,433	9,690
90+ days and still accruing	12,363	7,210	4,592
Loans, net of unearned income	4,937,408	4,855,487	3,958,543
Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
90+ days and still accruing	0	7	191
Loans, net of unearned income	7,354,163	7,042,810	6,111,495
Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	4	477	497
90+ days and still accruing	43	137	161
Loans, net of unearned income	48,519	24,199	35,983
Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	44,899	67,069	94,115
90+ days and still accruing	12,406	7,369	4,944
Loans, net of unearned income	35,230,451	34,758,276	33,119,392
60-89 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	35,730	53,666	28,005
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	0	0	0
60-89 days past due | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,294	23,492	13,292
60-89 days past due | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	0	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	499
60-89 days past due | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,648	284	7,657
60-89 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	199	0	492
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	293	982	944
60-89 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	8,890	15,490	5,113
60-89 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	22,401	12,614	0
60-89 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	5	34	8
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	35,730	53,666	28,005
30-59 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	118,589	187,423	151,704
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	185	275	0
30-59 days past due | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	31,873	42,933	35,535
30-59 days past due | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	16	928	6
30-59 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,409	2,809	23,967
30-59 days past due | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	28,732	37,634	46,201
30-59 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	545	1,120	780
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	18,808	12,145	13,768
30-59 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	21,278	22,419	16,552
30-59 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	15,522	66,651	14,821
30-59 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	221	509	74
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	118,404	187,148	151,704
Current
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	35,035,304	34,473,577	32,892,465
Current | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	16,292	30,553	51,841
Current | Commercial | Commercial, industrial and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	11,279,954	11,258,961	9,343,939
Current | Commercial | Commercial PPP loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	253,948	556,570	3,292,976
Current | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,393,943	1,352,018	1,326,185
Current | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	7,796,041	7,575,795	7,105,890
Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	318,944	331,461	383,445
Current | Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,723,526	1,576,704	1,333,867
Current | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	4,888,170	4,804,935	3,922,596
Current | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	7,316,240	6,963,538	6,096,483
Current | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	48,246	23,042	35,243
Current | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	$ 35,019,012	$ 34,443,024	$ 32,840,624