Loans and Allowance for Loan Losses - Classified as troubled debt restructurings (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) Contract	Sep. 30, 2019 USD ($) Contract	Sep. 30, 2020 USD ($) Contract	Sep. 30, 2019 USD ($) Contract
Commercial, Financial and Agricultural
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	10	4	21	10
Post-Modification Outstanding Recorded Investment | $	$ 104,864	$ 1,411	$ 170,579	$ 28,330
Number of subsequent default contracts | Contract	1	0	1	0
Recorded investment at subsequent default | $	$ 16,739	$ 0	$ 16,739	$ 0
Commercial Real Estate | Real estate – construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	0	0	0	0
Post-Modification Outstanding Recorded Investment | $	$ 0	$ 0	$ 0	$ 0
Number of subsequent default contracts | Contract	0	0	0	0
Recorded investment at subsequent default | $	$ 0	$ 0	$ 0	$ 0
Commercial Real Estate | Commercial real estate – mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	2	2	5	6
Post-Modification Outstanding Recorded Investment | $	$ 5,589	$ 18,115	$ 7,886	$ 20,638
Number of subsequent default contracts | Contract	0	1	0	1
Recorded investment at subsequent default | $	$ 0	$ 599	$ 0	$ 599
Residential Real Estate | Residential real estate – mortgage
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	19	29	34	65
Post-Modification Outstanding Recorded Investment | $	$ 6,706	$ 8,523	$ 8,528	$ 15,574
Number of subsequent default contracts | Contract	0	1	2	2
Recorded investment at subsequent default | $	$ 0	$ 234	$ 182	$ 455
Residential Real Estate | Equity lines of credit
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	5	3	13	5
Post-Modification Outstanding Recorded Investment | $	$ 168	$ 259	$ 567	$ 353
Number of subsequent default contracts | Contract	0	0	1	0
Recorded investment at subsequent default | $	$ 0	$ 0	$ 65	$ 0
Residential Real Estate | Equity loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	6	1	8	8
Post-Modification Outstanding Recorded Investment | $	$ 1,246	$ 49	$ 1,496	$ 456
Number of subsequent default contracts | Contract	1	0	1	2
Recorded investment at subsequent default | $	$ 270	$ 0	$ 270	$ 151
Consumer | Credit card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	0	0	0	0
Post-Modification Outstanding Recorded Investment | $	$ 0	$ 0	$ 0	$ 0
Number of subsequent default contracts | Contract	0	0	0	0
Recorded investment at subsequent default | $	$ 0	$ 0	$ 0	$ 0
Consumer | Consumer direct
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	42	110	176	178
Post-Modification Outstanding Recorded Investment | $	$ 2,545	$ 4,401	$ 10,656	$ 9,176
Number of subsequent default contracts | Contract	0	1	5	4
Recorded investment at subsequent default | $	$ 0	$ 600	$ 235	$ 2,610
Consumer | Consumer indirect
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Contracts | Contract	0	1	0	1
Post-Modification Outstanding Recorded Investment | $	$ 0	$ 2	$ 0	$ 2
Number of subsequent default contracts | Contract	0	0	0	0
Recorded investment at subsequent default | $	$ 0	$ 0	$ 0	$ 0