CAPITAL REQUIREMENTS AND RESTRICTIONS ON RETAINED EARNINGS - Financial Measures of Capital (Details)	Sep. 30, 2024	Sep. 30, 2023
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (core) capital (to adjusted total assets), ratio	9.26%	8.11%
Tier 1 (core) capital (to adjusted total assets), minimum requirement for capital adequacy purposes, ratio	4.00%	4.00%
Tier 1 (core) capital (to adjusted total assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio	5.00%	5.00%
Common equity Tier 1 (to risk-weighted assets), actual ratio	12.61%	11.25%
Common equity Tier 1 (to risk-weighted assets), minimum requirement for capital adequacy purposes, ratio	4.50%	4.50%
Common equity Tier 1 (to risk-weighted assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio	6.50%	6.50%
Tier 1 (core) capital ( to risk weighted assets), ratio	0.1286	0.1150
Tier 1 (core) capital (to risk-weighted assets), minimum requirement for capital adequacy purposes, ratio	0.0600	0.0600
Tier 1 (core) capital (to risk-weighted assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio	0.0800	0.0800
Total qualifying capital (to risk-weighted assets), ratio	14.08%	12.84%
Total qualifying capital (to risk-weighted assets), minimum requirement for capital adequacy purposes, ratio	8.00%	8.00%
Total qualifying capital (to risk-weighted assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio	10.00%	10.00%
MetaBank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (core) capital (to adjusted total assets), ratio	9.44%	8.32%
Common equity Tier 1 (to risk-weighted assets), actual ratio	13.12%	11.81%
Tier 1 (core) capital ( to risk weighted assets), ratio	0.1312	0.1181
Total qualifying capital (to risk-weighted assets), ratio	13.97%	12.76%