Allowance for Credit Losses (Schedule of Aging of the Company's Loan Portfolio) (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Financing Receivable, Past Due [Line Items]
Nonaccrual	$ 119,463	$ 98,379	$ 49,560
Loans, net of unearned income	39,565,471	39,196,485	35,280,547
Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Nonaccrual	29,245	31,279	4,661
Loans, net of unearned income	196,152	164,788	50,096
Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual	47,950	35,579	16,878
Loans, net of unearned income	12,576,985	12,549,164	11,583,963
Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	10,239,078	9,950,947	9,235,074
Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Nonaccrual	5,404	416	1,054
Loans, net of unearned income	1,597,053	1,486,930	1,396,406
Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Nonaccrual	5,792	5,971	11,247
Loans, net of unearned income	8,642,025	8,464,017	7,838,668
Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual	1,190	1,487	1,747
Loans, net of unearned income	337,016	332,698	321,435
Residential real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,505,545	2,372,383	1,799,985
Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	11,333	10,171	7,262
Loans, net of unearned income	2,309,393	2,207,595	1,749,889
Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	18,543	13,470	6,707
Loans, net of unearned income	5,738,880	5,849,459	4,937,408
Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
Loans, net of unearned income	8,125,802	8,090,998	7,354,163
Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	6	6	4
Loans, net of unearned income	42,165	50,836	48,519
Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	90,218	67,100	44,899
Loans, net of unearned income	39,369,319	39,031,697	35,230,451
90+ days and still accruing
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	47,392	81,047	41,364
90+ days and still accruing | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	36,920	47,450	28,958
90+ days and still accruing | Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	0	462	0
90+ days and still accruing | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	0	0	0
90+ days and still accruing | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	0	0	0
90+ days and still accruing | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	0	0	0
90+ days and still accruing | Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	104	0	0
90+ days and still accruing | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	9,215	15,841	12,363
90+ days and still accruing | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,066	17,245	0
90+ days and still accruing | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	87	49	43
90+ days and still accruing | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	10,472	33,597	12,406
60-89 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	67,333	48,924	35,730
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	984	0
60-89 days past due | Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	10,755	21,128	1,294
60-89 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	4,438	361	0
60-89 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	16,101	1,883	2,648
60-89 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	116	0	199
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	74	4,364	293
60-89 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	14,287	14,926	8,890
60-89 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	21,552	5,260	22,401
60-89 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	10	18	5
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	67,333	47,940	35,730
30-59 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	275,958	210,595	118,589
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	1,485	1,584	185
30-59 days past due | Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	95,593	56,696	31,889
30-59 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	19,616	14,390	1,409
30-59 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	53,064	16,285	28,732
30-59 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,118	2,152	545
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	19,183	9,982	18,808
30-59 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	32,545	40,557	21,278
30-59 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	52,975	68,725	15,522
30-59 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	379	224	221
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	274,473	209,011	118,404
Current
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	39,055,325	38,757,540	35,035,304
Current | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	128,502	83,491	16,292
Current | Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	12,422,687	12,435,299	11,533,902
Current | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,567,595	1,471,763	1,393,943
Current | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	8,567,068	8,439,878	7,796,041
Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	334,592	329,059	318,944
Current | Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,278,699	2,183,078	1,723,526
Current | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	5,664,290	5,764,665	4,888,170
Current | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	8,050,209	7,999,768	7,316,240
Current | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	41,683	50,539	48,246
Current | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	$ 38,926,823	$ 38,674,049	$ 35,019,012