Allowance for Credit Losses - Roll Forward Of the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Allowance for credit losses:
Beginning balance	$ 198,578	$ 192,090	$ 192,090
Charge-offs	(910)	(6,457)	(19,040)
Recoveries	746	1,725
Net (charge-offs) recoveries	(164)	(4,732)
Provision for (recovery of) credit losses on loans	2,638	7,960
Ending balance	201,052	195,292	198,578
Individually evaluated	9,947	16,809
Collectively evaluated	191,105	178,483
Loans:
Individually evaluated	36,491	48,923
Collectively evaluated	12,464,034	11,717,502
Loans, net of unearned income	12,500,525	11,766,425	12,351,230
Nonaccruing loans with no allowance for credit losses	17,615	15,994
Commercial, financial, agricultural
Allowance for credit losses:
Beginning balance	43,980	44,255	44,255
Charge-offs	(349)	(529)	(8,838)
Recoveries	346	725
Net (charge-offs) recoveries	(3)	196
Provision for (recovery of) credit losses on loans	1,944	253
Ending balance	45,921	44,678	43,980
Individually evaluated	9,104	14,162
Collectively evaluated	36,817	30,516
Loans:
Individually evaluated	15,861	24,985
Collectively evaluated	1,853,547	1,715,793
Loans, net of unearned income	1,869,408	1,740,778
Nonaccruing loans with no allowance for credit losses	157	768
Real estate – construction:
Allowance for credit losses:
Beginning balance	18,612	19,114	19,114
Charge-offs	0	0
Recoveries	0	0
Net (charge-offs) recoveries	0	0
Provision for (recovery of) credit losses on loans	(1,295)	845
Ending balance	17,317	19,959	18,612
Individually evaluated	0	35
Collectively evaluated	17,317	19,924
Loans:
Individually evaluated	0	652
Collectively evaluated	1,243,535	1,423,700
Loans, net of unearned income	1,243,535	1,424,352
Nonaccruing loans with no allowance for credit losses	0	0
Real estate – 1-4 family mortgage:
Allowance for credit losses:
Beginning balance	47,283	44,727	44,727
Charge-offs	(82)	(3)	(417)
Recoveries	48	24
Net (charge-offs) recoveries	(34)	21
Provision for (recovery of) credit losses on loans	317	1,233
Ending balance	47,566	45,981	47,283
Individually evaluated	0	608
Collectively evaluated	47,566	45,373
Loans:
Individually evaluated	7,327	12,637
Collectively evaluated	3,421,959	3,266,343
Loans, net of unearned income	3,429,286	3,278,980
Nonaccruing loans with no allowance for credit losses	7,328	9,710
Real estate – commercial mortgage:
Allowance for credit losses:
Beginning balance	77,020	71,798	71,798
Charge-offs	0	(5,115)	(5,568)
Recoveries	6	211
Net (charge-offs) recoveries	6	(4,904)
Provision for (recovery of) credit losses on loans	1,699	5,876
Ending balance	78,725	72,770	77,020
Individually evaluated	573	1,734
Collectively evaluated	78,152	71,036
Loans:
Individually evaluated	13,033	10,375
Collectively evaluated	5,740,197	5,075,438
Loans, net of unearned income	5,753,230	5,085,813
Nonaccruing loans with no allowance for credit losses	10,130	5,511
Lease financing
Allowance for credit losses:
Beginning balance	2,515	2,463	2,463
Charge-offs	0	0	(1,524)
Recoveries	8	5
Net (charge-offs) recoveries	8	5
Provision for (recovery of) credit losses on loans	31	(31)
Ending balance	2,554	2,437	2,515
Individually evaluated	0	0
Collectively evaluated	2,554	2,437
Loans:
Individually evaluated	0	0
Collectively evaluated	107,474	121,146
Loans, net of unearned income	107,474	121,146
Nonaccruing loans with no allowance for credit losses	0	0
Installment Loans to Individuals
Allowance for credit losses:
Beginning balance	9,168	9,733	9,733
Charge-offs	(479)	(810)	(2,636)
Recoveries	338	760
Net (charge-offs) recoveries	(141)	(50)
Provision for (recovery of) credit losses on loans	(58)	(216)
Ending balance	8,969	9,467	9,168
Individually evaluated	270	270
Collectively evaluated	8,699	9,197
Loans:
Individually evaluated	270	274
Collectively evaluated	97,322	115,082
Loans, net of unearned income	97,592	115,356
Nonaccruing loans with no allowance for credit losses	$ 0	5
Cumulative Effect, Period Of Adoption, Adjustment
Allowance for credit losses:
Beginning balance		(26)	(26)
Cumulative Effect, Period Of Adoption, Adjustment \| Commercial, financial, agricultural
Allowance for credit losses:
Beginning balance		(26)	(26)
Cumulative Effect, Period Of Adoption, Adjustment \| Real estate – construction:
Allowance for credit losses:
Beginning balance		0	0
Cumulative Effect, Period Of Adoption, Adjustment \| Real estate – 1-4 family mortgage:
Allowance for credit losses:
Beginning balance		0	0
Cumulative Effect, Period Of Adoption, Adjustment \| Real estate – commercial mortgage:
Allowance for credit losses:
Beginning balance		0	0
Cumulative Effect, Period Of Adoption, Adjustment \| Lease financing
Allowance for credit losses:
Beginning balance		0	0
Cumulative Effect, Period Of Adoption, Adjustment \| Installment Loans to Individuals
Allowance for credit losses:
Beginning balance		$ 0	$ 0

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

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Amount, excluding accrued interest, of decrease (increase) in allowance for credit loss on financing receivable from writeoff (recovery). Excludes net investment in lease.

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Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

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Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

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Amortized cost excluding accrued interest, of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease.

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The balance of financing receivables that were individually evaluated for impairment.

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