Long-term Debt - Schedule of long-term debt (Details) - USD ($) $ in Thousands	12 Months Ended	29 Months Ended		64 Months Ended	67 Months Ended	71 Months Ended
	Dec. 31, 2021	Dec. 31, 2027	Dec. 31, 2022	Dec. 31, 2026	Dec. 31, 2030	Dec. 31, 2028	Dec. 31, 2020
Debt Instrument [Line Items]
Less net discount	$ (8,260)						$ (9,296)
Total long-term debt	247,360						326,956
Senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	135,000						185,000
Senior debentures | 2022 senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 0						50,000
Interest Rate (percent)	5.00%
Senior debentures | 2022 senior debentures | LIBOR | Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (percent)			3.814%
Senior debentures | 2027 senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 35,000						35,000
Interest Rate (percent)	5.50%
Senior debentures | 2027 senior debentures | LIBOR | Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (percent)		3.71%
Senior debentures | 2030 senior debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000						100,000
Interest Rate (percent)	5.00%
Senior debentures | 2030 senior debentures | SOFR | Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (percent)					4.87%
Subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000						111,250
Subordinated debentures | 2026 subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 0						15,000
Interest Rate (percent)	5.875%
Subordinated debentures | 2026 subordinated debentures | LIBOR | Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (percent)				4.70%
Subordinated debentures | 2028 subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 100,000						100,000
Interest Rate (percent)	4.50%
Subordinated debentures | 2028 subordinated debentures | LIBOR | Forecast
Debt Instrument [Line Items]
Basis spread on variable rate (percent)						2.12%
Subordinated debentures | 2025 subordinated debentures
Debt Instrument [Line Items]
Long-term debt, gross	$ 0						11,250
Interest Rate (percent)	6.25%
Trust preferred securities
Debt Instrument [Line Items]
Long-term debt, gross	$ 20,620						25,002
Trust preferred securities | Southern Bancorp Capital Trust I
Debt Instrument [Line Items]
Long-term debt, gross	$ 0						4,382
Trust preferred securities | Southern Bancorp Capital Trust I | Prime Rate
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.00%
Trust preferred securities | Tidelands Statutory Trust I
Debt Instrument [Line Items]
Long-term debt, gross	$ 8,248						8,248
Trust preferred securities | Tidelands Statutory Trust I | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.38%
Trust preferred securities | Four Oaks Statutory Trust I
Debt Instrument [Line Items]
Long-term debt, gross	$ 12,372						$ 12,372
Trust preferred securities | Four Oaks Statutory Trust I | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	1.35%