Allowance for Loan Losses - Roll Forward Of the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Allowance for loan losses:
Beginning balance	$ 52,162	$ 49,026
Charge-offs	(5,349)	(1,537)
Recoveries	4,538	846
Net (charge-offs) recoveries	(811)	(691)
Provision for credit losses on loans	26,350	1,500
Ending balance	120,185	49,835
Loans:
Individually evaluated	27,186		$ 51,179
Collectively evaluated	9,742,191		9,466,195
Ending balance	9,769,377		9,689,638
Nonaccruing loans with no allowance for credit losses	12,855
Individually evaluated	5,149	2,213
Collectively evaluated	115,036	45,098
Purchased with deteriorated credit quality
Allowance for loan losses:
Ending balance		2,524
Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	10,658	8,269
Charge-offs	(393)	(258)
Recoveries	190	374
Net (charge-offs) recoveries	(203)	116
Provision for credit losses on loans	4,131	1,237
Ending balance	25,937	9,622
Loans:
Individually evaluated	10,460		8,460
Collectively evaluated	1,414,116		1,329,974
Ending balance	1,424,576
Nonaccruing loans with no allowance for credit losses	4,224
Individually evaluated	3,653	1,181
Collectively evaluated	22,284	8,312
Commercial, financial, agricultural \| Purchased with deteriorated credit quality
Allowance for loan losses:
Ending balance		129
Real estate – construction:
Allowance for loan losses:
Beginning balance	5,029	4,755
Charge-offs	0	0
Recoveries	0	7
Net (charge-offs) recoveries	0	7
Provision for credit losses on loans	2,390	16
Ending balance	10,924	4,778
Loans:
Individually evaluated	2,728		12,416
Collectively evaluated	785,167		813,204
Ending balance	787,895
Nonaccruing loans with no allowance for credit losses	2,728
Individually evaluated	0	58
Collectively evaluated	10,924	4,720
Real estate – construction: \| Purchased with deteriorated credit quality
Allowance for loan losses:
Ending balance		0
Real estate – 1-4 family mortgage
Allowance for loan losses:
Beginning balance	9,814	10,139
Charge-offs	(221)	(497)
Recoveries	88	197
Net (charge-offs) recoveries	(133)	(300)
Provision for credit losses on loans	3,325	(348)
Ending balance	27,320	9,491
Loans:
Individually evaluated	5,865		20,262
Collectively evaluated	2,840,436		2,810,808
Ending balance	2,846,301
Nonaccruing loans with no allowance for credit losses	3,309
Individually evaluated	370	127
Collectively evaluated	26,950	8,944
Real estate – 1-4 family mortgage \| Purchased with deteriorated credit quality
Allowance for loan losses:
Ending balance		420
Real estate – commercial mortgage:
Allowance for loan losses:
Beginning balance	24,990	24,492
Charge-offs	(2,047)	(562)
Recoveries	1,699	245
Net (charge-offs) recoveries	(348)	(317)
Provision for credit losses on loans	15,302	468
Ending balance	44,237	24,643
Loans:
Individually evaluated	7,508		9,550
Collectively evaluated	4,301,200		4,131,582
Ending balance	4,308,708
Nonaccruing loans with no allowance for credit losses	2,594
Individually evaluated	856	842
Collectively evaluated	43,381	21,828
Real estate – commercial mortgage: \| Purchased with deteriorated credit quality
Allowance for loan losses:
Ending balance		1,973
Lease financing
Allowance for loan losses:
Beginning balance	910
Charge-offs	0
Recoveries	5
Net (charge-offs) recoveries	5
Provision for credit losses on loans	152
Ending balance	1,588
Loans:
Individually evaluated	0
Collectively evaluated	84,679
Ending balance	84,679
Nonaccruing loans with no allowance for credit losses	0
Individually evaluated	0
Collectively evaluated	1,588
Installment and Other
Allowance for loan losses:
Beginning balance	761	1,371
Charge-offs	(2,688)	(220)
Recoveries	2,556	23
Net (charge-offs) recoveries	(132)	(197)
Provision for credit losses on loans	1,050	127
Ending balance	10,179	1,301
Loans:
Individually evaluated	625		491
Collectively evaluated	316,593		$ 380,627
Ending balance	317,218
Nonaccruing loans with no allowance for credit losses	0
Individually evaluated	270	5
Collectively evaluated	9,909	1,294
Installment and Other \| Purchased with deteriorated credit quality
Allowance for loan losses:
Ending balance		$ 2
Cumulative Effect, Period Of Adoption, Adjustment
Allowance for loan losses:
Beginning balance	42,484
Cumulative Effect, Period Of Adoption, Adjustment \| Commercial, financial, agricultural
Allowance for loan losses:
Beginning balance	11,351
Cumulative Effect, Period Of Adoption, Adjustment \| Real estate – construction:
Allowance for loan losses:
Beginning balance	3,505
Cumulative Effect, Period Of Adoption, Adjustment \| Real estate – 1-4 family mortgage
Allowance for loan losses:
Beginning balance	14,314
Cumulative Effect, Period Of Adoption, Adjustment \| Real estate – commercial mortgage:
Allowance for loan losses:
Beginning balance	4,293
Cumulative Effect, Period Of Adoption, Adjustment \| Lease financing
Allowance for loan losses:
Beginning balance	521
Cumulative Effect, Period Of Adoption, Adjustment \| Installment and Other
Allowance for loan losses:
Beginning balance	$ 8,500

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Amount, after recovery, of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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