Stockholders' Equity and Regulatory Capital (Details) $ in Thousands	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)
Southern Bank \| Total Capital (to Risk-Weighted Assets)
Stockholders' Equity and Regulatory Capital
Capital	$ 592,351	$ 545,293
Capital to Risk Weighted Assets	0.1337	0.1334
Capital Required for Capital Adequacy	$ 354,515	$ 326,920
Capital Required for Capital Adequacy to Risk Weighted Assets	0.08	0.08
Capital Required to be Well Capitalized	$ 443,143	$ 408,650
Capital Required to be Well Capitalized to Risk Weighted Assets	0.10	0.10
Southern Bank \| Tier I Capital (to Risk-Weighted Assets)
Stockholders' Equity and Regulatory Capital
Capital	$ 536,920	$ 494,186
Capital to Risk Weighted Assets	0.1212	0.1209
Capital Required for Capital Adequacy	$ 265,886	$ 245,190
Capital Required for Capital Adequacy to Risk Weighted Assets	0.06	0.06
Capital Required to be Well Capitalized	$ 354,515	$ 326,920
Capital Required to be Well Capitalized to Risk Weighted Assets	0.08	0.08
Southern Bank \| Tier I Capital (to Average Assets)
Stockholders' Equity and Regulatory Capital
Capital	$ 536,920	$ 494,186
Capital to Risk Weighted Assets	0.1045	0.1005
Capital Required for Capital Adequacy	$ 205,606	$ 196,782
Capital Required for Capital Adequacy to Risk Weighted Assets	0.04	0.04
Capital Required to be Well Capitalized	$ 257,007	$ 245,977
Capital Required to be Well Capitalized to Risk Weighted Assets	0.05	0.05
Southern Bank \| Common Equity Tier I Capital (to Risk-Weighted Assets)
Stockholders' Equity and Regulatory Capital
Capital	$ 536,920	$ 494,186
Capital to Risk Weighted Assets	0.1212	0.1209
Capital Required for Capital Adequacy	$ 199,414	$ 183,892
Capital Required for Capital Adequacy to Risk Weighted Assets	0.045	0.045
Capital Required to be Well Capitalized	$ 288,043	$ 265,622
Capital Required to be Well Capitalized to Risk Weighted Assets	0.065	0.065
Consolidated \| Total Capital (to Risk-Weighted Assets)
Stockholders' Equity and Regulatory Capital
Capital	$ 618,987	$ 577,150
Capital to Risk Weighted Assets	0.1381	0.1395
Capital Required for Capital Adequacy	$ 358,650	$ 331,050
Capital Required for Capital Adequacy to Risk Weighted Assets	0.08	0.08
Consolidated \| Tier I Capital (to Risk-Weighted Assets)
Stockholders' Equity and Regulatory Capital
Capital	$ 562,917	$ 517,842
Capital to Risk Weighted Assets	0.1256	0.1251
Capital Required for Capital Adequacy	$ 268,988	$ 248,288
Capital Required for Capital Adequacy to Risk Weighted Assets	0.06	0.06
Consolidated \| Tier I Capital (to Average Assets)
Stockholders' Equity and Regulatory Capital
Capital	$ 562,917	$ 517,842
Capital to Risk Weighted Assets	0.1103	0.1061
Capital Required for Capital Adequacy	$ 204,072	$ 195,249
Capital Required for Capital Adequacy to Risk Weighted Assets	0.04	0.04
Consolidated \| Common Equity Tier I Capital (to Risk-Weighted Assets)
Stockholders' Equity and Regulatory Capital
Capital	$ 547,151	$ 502,197
Capital to Risk Weighted Assets	0.122	0.1214
Capital Required for Capital Adequacy	$ 201,741	$ 186,216
Capital Required for Capital Adequacy to Risk Weighted Assets	0.045	0.045

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-Section 50
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