Loans - Schedule of composition of loan portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 7,177,785	$ 6,501,404
Interest Receivable	20,653	19,221
Loans and Leases Receivable, Recorded Investment	7,198,438	6,520,625
Commercial Financial And Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,588,989	1,185,110
Interest Receivable	6,528	4,393
Loans and Leases Receivable, Recorded Investment	1,595,517	1,189,503
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,748,189	1,609,413
Interest Receivable	6,017	5,571
Loans and Leases Receivable, Recorded Investment	1,754,206	1,614,984
Construction Real Estate Remaining Commercial [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	226,991	233,637
Interest Receivable	572	826
Loans and Leases Receivable, Recorded Investment	227,563	234,463
Construction Real Estate Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	115,492	96,574
Interest Receivable	232	228
Loans and Leases Receivable, Recorded Investment	115,724	96,802
Construction Real Estate Installment [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	938	1,488
Interest Receivable	3	4
Loans and Leases Receivable, Recorded Investment	941	1,492
Residential Real Estate Commercial [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	526,222	479,081
Interest Receivable	1,161	1,339
Loans and Leases Receivable, Recorded Investment	527,383	480,420
Residential Real Estate Mortgage [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,096,358	1,176,316
Interest Receivable	947	1,381
Loans and Leases Receivable, Recorded Investment	1,097,305	1,177,697
Residential Real Estate Home Equity Line Of Credit [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	182,028	224,766
Interest Receivable	647	1,113
Loans and Leases Receivable, Recorded Investment	182,675	225,879
Residential Real Estate Installment [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	8,436	12,563
Interest Receivable	22	32
Loans and Leases Receivable, Recorded Investment	8,458	12,595
Consumer Portfolio Segment [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,659,704	1,452,375
Interest Receivable	4,510	4,314
Loans and Leases Receivable, Recorded Investment	1,664,214	1,456,689
Leases
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Net of Deferred Income	24,438	30,081
Interest Receivable	14	20
Loans and Leases Receivable, Recorded Investment	$ 24,452	$ 30,101

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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
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