CAPITAL REQUIREMENTS AND RESTRICTIONS ON RETAINED EARNINGS - Financial Measures of Capital (Details)	Sep. 30, 2017	Sep. 30, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (core) capital (to adjusted total assets), ratio	7.64%	17.28%
Tier 1 (core) capital (to adjusted total assets), minimum requirement for capital adequacy purposes, ratio	4.00%	4.50%
Tier 1 (core) capital (to adjusted total assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio	5.00%	6.50%
Common equity Tier 1 (to risk-weighted assets), actual ratio	13.97%
Common equity Tier 1 (to risk-weighted assets), minimum requirement for capital adequacy purposes, ratio	4.50%
Common equity Tier 1 (to risk-weighted assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio	6.50%
Tangible capital (to tangible assets), actual ratio		8.35%
Tangible capital (to tangible assets), minimum requirement for capital adequacy purposes, ratio		4.00%
Tangible capital (to tangible assets), minimum requirement to be well capitalized under prompt corrective actions provisions, ratio		5.00%
Tier 1 (core) capital ( to risk weighted assets), ratio	14.46%	17.82%
Tier 1 (core) capital (to risk-weighted assets), minimum requirement for capital adequacy purposes, ratio	6.00%	6.00%
Tier 1 (core) capital (to risk-weighted assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio	8.00%	8.00%
Total qualifying capital (to risk-weighted assets), ratio	18.41%
Total qualifying capital (to risk-weighted assets), minimum requirement for capital adequacy purposes, ratio	8.00%
Total qualifying capital (to risk-weighted assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio	10.00%
Total risk based capital (to risk weighted assets), ratio		23.17%
Total risk based capital (to risk weighted assets), minimum requirement for capital adequacy purposes, ratio		8.00%
Total risk based capital (to risk weighted assets), minimum requirement to be well capitalized under prompt corrective action provisions, ratio		10.00%
MetaBank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 (core) capital (to adjusted total assets), ratio	9.64%	21.95%
Common equity Tier 1 (to risk-weighted assets), actual ratio	18.22%
Tangible capital (to tangible assets), actual ratio		10.35%
Tier 1 (core) capital ( to risk weighted assets), ratio	18.22%	21.95%
Total qualifying capital (to risk-weighted assets), ratio	18.59%
Total risk based capital (to risk weighted assets), ratio		22.35%