Stockholders' Equity and Regulatory Capital (Details) $ in Thousands	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)
Southern Bank | Total Capital (to Risk-Weighted Assets)
Capital	$ 352,169	$ 308,482
Capital to Risk Weighted Assets	12.90	13.96
Capital Required for Capital Adequacy	$ 218,397	$ 176,816
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00	8.00
Capital Required to be Well Capitalized	$ 272,996	$ 221,019
Capital Required to be Well Capitalized to Risk Weighted Assets	10.00	10.00
Southern Bank | Tier I Capital (to Risk-Weighted Assets)
Capital	$ 325,183	$ 282,638
Capital to Risk Weighted Assets	11.91	12.79
Capital Required for Capital Adequacy	$ 163,797	$ 132,612
Capital Required for Capital Adequacy to Risk Weighted Assets	6.00	6.00
Capital Required to be Well Capitalized	$ 218,397	$ 176,816
Capital Required to be Well Capitalized to Risk Weighted Assets	8.00	8.00
Southern Bank | Tier I Capital (to Average Assets)
Capital	$ 325,183	$ 282,638
Capital to Risk Weighted Assets	10.22	10.43
Capital Required for Capital Adequacy	$ 127,333	$ 108,369
Capital Required for Capital Adequacy to Risk Weighted Assets	4.00	4.00
Capital Required to be Well Capitalized	$ 159,167	$ 135,461
Capital Required to be Well Capitalized to Risk Weighted Assets	5.00	5.00
Southern Bank | Common Equity Tier I Capital (to Risk-Weighted Assets)
Capital	$ 325,183	$ 282,638
Capital to Risk Weighted Assets	11.91	12.79
Capital Required for Capital Adequacy	$ 122,848	$ 99,459
Capital Required for Capital Adequacy to Risk Weighted Assets	4.50	4.50
Capital Required to be Well Capitalized	$ 177,447	$ 143,663
Capital Required to be Well Capitalized to Risk Weighted Assets	6.50	6.50
Consolidated | Total Capital (to Risk-Weighted Assets)
Capital	$ 370,013	$ 315,490
Capital to Risk Weighted Assets	13.42	14.18
Capital Required for Capital Adequacy	$ 220,558	$ 177,938
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00	8.00
Consolidated | Tier I Capital (to Risk-Weighted Assets)
Capital	$ 335,316	$ 287,701
Capital to Risk Weighted Assets	12.16	12.93
Capital Required for Capital Adequacy	$ 165,418	$ 133,453
Capital Required for Capital Adequacy to Risk Weighted Assets	6.00	6.00
Consolidated | Tier I Capital (to Average Assets)
Capital	$ 335,316	$ 287,701
Capital to Risk Weighted Assets	10.41	10.61
Capital Required for Capital Adequacy	$ 128,822	$ 108,505
Capital Required for Capital Adequacy to Risk Weighted Assets	4.00	4.00
Consolidated | Common Equity Tier I Capital (to Risk-Weighted Assets)
Capital	$ 319,971	$ 272,458
Capital to Risk Weighted Assets	11.61	12.25
Capital Required for Capital Adequacy	$ 124,064	$ 100,090
Capital Required for Capital Adequacy to Risk Weighted Assets	4.50	4.50