Allowance for Credit Losses - Schedule of Aging of the Company's Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Financing Receivable, Past Due [Line Items]
Nonaccrual	$ 149,566	$ 154,641	$ 161,059
Total loans, net of unearned income	52,063,482	48,055,037	47,067,447
Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	0	0
Total loans, net of unearned income	124,824	156,756	135,389
Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual	66,577	73,490	63,826
Total loans, net of unearned income	16,544,342	15,574,551	15,247,693
Commercial real estate
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	13,619,207	12,903,944	12,793,417
Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Nonaccrual	3,227	2,282	2,284
Total loans, net of unearned income	2,658,153	2,434,081	2,403,690
Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Nonaccrual	24,975	18,760	39,787
Total loans, net of unearned income	10,961,054	10,469,863	10,389,727
Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual	1,295	1,117	1,122
Total loans, net of unearned income	484,202	445,028	427,043
Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	4,143,870	3,612,765	3,388,038
Residential real estate, excluding early buy-out loans | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	28,942	23,762	17,959
Total loans, net of unearned income	4,019,046	3,456,009	3,252,649
Premium finance receivables | Premium finance receivables—property & casualty
Financing Receivable, Past Due [Line Items]
Nonaccrual	24,512	28,797	36,079
Total loans, net of unearned income	8,366,292	7,272,042	7,131,681
Premium finance receivables | Premium finance receivables—life insurance
Financing Receivable, Past Due [Line Items]
Nonaccrual	0	6,431	0
Total loans, net of unearned income	8,758,553	8,147,145	7,996,899
Consumer and other
Financing Receivable, Past Due [Line Items]
Nonaccrual	38	2	2
Total loans, net of unearned income	147,016	99,562	82,676
Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Nonaccrual	149,566	154,641	161,059
Total loans, net of unearned income	51,938,658	47,898,281	46,932,058
90+ days and still accruing
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	60,440	50,134	61,986
90+ days and still accruing | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	47,374	33,952	43,358
90+ days and still accruing | Commercial
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	0	104	20
90+ days and still accruing | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	0	0	0
90+ days and still accruing | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	0	0	225
90+ days and still accruing | Home equity
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	0	0	0
90+ days and still accruing | Residential real estate, excluding early buy-out loans | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	0	0	0
90+ days and still accruing | Premium finance receivables | Premium finance receivables—property & casualty
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	13,006	16,031	18,235
90+ days and still accruing | Premium finance receivables | Premium finance receivables—life insurance
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	0	0	0
90+ days and still accruing | Consumer and other
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	60	47	148
90+ days and still accruing | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	13,066	16,182	18,628
60-89 days past due
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	92,976	164,988	83,212
60-89 days past due | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	0	618	150
60-89 days past due | Commercial
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	12,190	54,844	32,560
60-89 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	630	1,339	757
60-89 days past due | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	13,489	9,182	12,682
60-89 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	246	1,233	1,035
60-89 days past due | Residential real estate, excluding early buy-out loans | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	8,829	5,708	6,364
60-89 days past due | Premium finance receivables | Premium finance receivables—property & casualty
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	23,527	19,042	18,740
60-89 days past due | Premium finance receivables | Premium finance receivables—life insurance
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	34,016	72,963	10,902
60-89 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	49	59	22
60-89 days past due | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	92,976	164,370	83,062
30-59 days past due
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	194,378	252,223	204,043
30-59 days past due | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	0	2,335	0
30-59 days past due | Commercial
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	36,136	92,551	46,057
30-59 days past due | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	40,276	4,634	1,798
30-59 days past due | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	42,779	26,132	46,548
30-59 days past due | Home equity
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	2,294	2,148	2,580
30-59 days past due | Residential real estate, excluding early buy-out loans | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	95	18,917	2,160
30-59 days past due | Premium finance receivables | Premium finance receivables—property & casualty
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	38,133	68,219	30,204
30-59 days past due | Premium finance receivables | Premium finance receivables—life insurance
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	34,506	36,405	74,432
30-59 days past due | Consumer and other
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	159	882	264
30-59 days past due | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	194,378	249,888	204,043
Current
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	51,566,122	47,433,051	46,557,147
Current | Early buy-out loans guaranteed by U.S. government agencies
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	77,450	119,851	91,881
Current | Commercial
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	16,429,439	15,353,562	15,105,230
Current | Commercial real estate | Construction and development
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	2,614,020	2,425,826	2,398,851
Current | Commercial real estate | Non-construction
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	10,879,811	10,415,789	10,290,485
Current | Home equity
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	480,367	440,530	422,306
Current | Residential real estate, excluding early buy-out loans | Residential real estate, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	3,981,180	3,407,622	3,226,166
Current | Premium finance receivables | Premium finance receivables—property & casualty
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	8,267,114	7,139,953	7,028,423
Current | Premium finance receivables | Premium finance receivables—life insurance
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	8,690,031	8,031,346	7,911,565
Current | Consumer and other
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	146,710	98,572	82,240
Current | Total loans, net of unearned income, excluding early buy-out loans
Financing Receivable, Past Due [Line Items]
Total loans, net of unearned income	$ 51,488,672	$ 47,313,200	$ 46,465,266