Allowance for Credit Losses - Schedule of Aging of the Company's Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Financing Receivable, Past Due [Line Items]
Nonaccrual	$ 104,967	$ 98,379	$ 102,930
Loans, net of unearned income	41,446,032	39,196,485	38,167,613
Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Nonaccrual	117	31,279	24,020
Loans, net of unearned income	168,973	164,788	148,664
Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual	43,569	35,579	44,293
Loans, net of unearned income	12,725,473	12,549,164	12,259,250
Commercial real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	10,946,180	9,950,947	9,578,184
Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Nonaccrual	8,384	416	889
Loans, net of unearned income	1,893,773	1,486,930	1,525,511
Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Nonaccrual	8,659	5,971	9,588
Loans, net of unearned income	9,052,407	8,464,017	8,052,673
Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual	1,363	1,487	1,320
Loans, net of unearned income	343,258	332,698	328,822
Residential real estate
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,707,603	2,372,383	2,235,459
Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	16,103	10,171	9,787
Loans, net of unearned income	2,538,630	2,207,595	2,086,795
Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	26,756	13,470	13,026
Loans, net of unearned income	6,722,747	5,849,459	5,713,340
Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
Loans, net of unearned income	7,931,808	8,090,998	8,004,856
Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	16	6	7
Loans, net of unearned income	68,963	50,836	47,702
Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	104,850	67,100	78,910
Loans, net of unearned income	41,277,059	39,031,697	38,018,949
90+ days and still accruing
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	85,809	81,047	86,790
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	57,558	47,450	68,067
90+ days and still accruing | Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	200	462	237
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	1,092	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	0	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	16,253	15,841	16,624
90+ days and still accruing | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	10,679	17,245	1,831
90+ days and still accruing | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	27	49	31
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	28,251	33,597	18,723
60-89 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	92,406	48,924	62,400
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	2,116	984	489
60-89 days past due | Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	22,889	21,128	24,641
60-89 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,438	361	0
60-89 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	4,957	1,883	6,041
60-89 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	219	0	125
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	1,145	4,364	2,149
60-89 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	16,552	14,926	15,301
60-89 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	41,894	5,260	13,628
60-89 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	196	18	26
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	90,290	47,940	61,911
30-59 days past due
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	146,647	210,595	132,280
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	1,584	104
30-59 days past due | Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	35,681	56,696	34,917
30-59 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	31,292	14,390	5,715
30-59 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	29,692	16,285	24,256
30-59 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,668	2,152	848
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	904	9,982	15
30-59 days past due | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	31,919	40,557	21,128
30-59 days past due | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	14,972	68,725	44,954
30-59 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	519	224	343
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	146,647	209,011	132,176
Current
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	41,016,203	38,757,540	37,783,213
Current | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	109,182	83,491	55,984
Current | Commercial
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	12,623,134	12,435,299	12,155,162
Current | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	1,851,659	1,471,763	1,518,907
Current | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	9,008,007	8,439,878	8,012,788
Current | Home equity
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	340,008	329,059	326,529
Current | Residential real estate | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	2,520,478	2,183,078	2,074,844
Current | Premium finance receivables | Property and casualty insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	6,631,267	5,764,665	5,647,261
Current | Premium finance receivables | Life insurance loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	7,864,263	7,999,768	7,944,443
Current | Consumer and other
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	68,205	50,539	47,295
Current | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Loans, net of unearned income	$ 40,907,021	$ 38,674,049	$ 37,727,229