LOANS AND LEASES RECEIVABLE, NET - Past Due Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	$ 2,944,989	$ 1,326,832
Impaired financing receivable, interest income, accrual method	100
National Lending [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	1,846,283	395,729
National Lending [Member] | Commercial Operating [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	1,509,849	255,308
National Lending [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	335,361	140,229
National Lending [Member] | Tax Services [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	1,073	192
Community Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	1,098,706	931,103
Community Banking [Member] | Commercial Operating [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	42,311	30,718
Community Banking [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	23,836	22,775
Community Banking [Member] | Commercial and Multi-Family Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	748,579	585,510
Community Banking [Member] | 1-4 Family Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	223,482	196,706
Community Banking [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans receivable	60,498	95,394
Accruing and Non-accruing Loans and Lease [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	38,851	45,061
Current	2,906,138	1,281,771
Total loans receivable	2,944,989	1,326,832
Accruing and Non-accruing Loans and Lease [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	24,022	4,686
Accruing and Non-accruing Loans and Lease [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,297	3,079
Accruing and Non-accruing Loans and Lease [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	9,532	37,296
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	38,667	9,587
Current	1,807,616	386,142
Total loans receivable	1,846,283	395,729
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	23,917	4,012
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,297	2,983
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	9,453	2,592
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Commercial Operating [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	30,406	5,156
Current	1,479,443	250,152
Total loans receivable	1,509,849	255,308
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Commercial Operating [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	20,708	1,509
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Commercial Operating [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,702	2,442
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Commercial Operating [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,996	1,205
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	7,188	4,431
Current	328,173	135,798
Total loans receivable	335,361	140,229
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	3,209	2,503
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,595	541
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Consumer [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	2,384	1,387
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Tax Services [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,073	0
Current	0	192
Total loans receivable	1,073	192
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Tax Services [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Tax Services [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Accruing and Non-accruing Loans and Lease [Member] | National Lending [Member] | Tax Services [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	1,073	0
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	184	35,474
Current	1,098,522	895,629
Total loans receivable	1,098,706	931,103
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	105	674
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	96
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	79	34,704
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Commercial Operating [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Current	42,311	30,718
Total loans receivable	42,311	30,718
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Commercial Operating [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Commercial Operating [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Commercial Operating [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	45
Current	23,836	22,730
Total loans receivable	23,836	22,775
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	9
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	17
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Consumer [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	19
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Commercial and Multi-Family Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	685
Current	748,579	584,825
Total loans receivable	748,579	585,510
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Commercial and Multi-Family Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	295
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Commercial and Multi-Family Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Commercial and Multi-Family Real Estate [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	390
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | 1-4 Family Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	184	449
Current	223,298	196,257
Total loans receivable	223,482	196,706
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | 1-4 Family Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	105	370
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | 1-4 Family Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	79
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | 1-4 Family Real Estate [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	79	0
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	34,295
Current	60,498	61,099
Total loans receivable	60,498	95,394
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Agricultural [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Agricultural [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	0
Accruing and Non-accruing Loans and Lease [Member] | Community Banking [Member] | Agricultural [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	0	34,295
Non-performing Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	2,864	685
Total loans receivable	10,201	37,591
Non-performing Loans and Leases [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	7,337	36,906
Non-performing Loans and Leases [Member] | National Lending [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	2,864	0
Total loans receivable	10,122	2,592
Non-performing Loans and Leases [Member] | National Lending [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	7,258	2,592
Non-performing Loans and Leases [Member] | National Lending [Member] | Commercial Operating [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	2,864	0
Total loans receivable	6,665	1,205
Non-performing Loans and Leases [Member] | National Lending [Member] | Commercial Operating [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	3,801	1,205
Non-performing Loans and Leases [Member] | National Lending [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	0
Total loans receivable	2,384	1,387
Non-performing Loans and Leases [Member] | National Lending [Member] | Consumer [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	2,384	1,387
Non-performing Loans and Leases [Member] | National Lending [Member] | Tax Services [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	0
Total loans receivable	1,073	0
Non-performing Loans and Leases [Member] | National Lending [Member] | Tax Services [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	1,073	0
Non-performing Loans and Leases [Member] | Community Banking [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	685
Total loans receivable	79	34,999
Non-performing Loans and Leases [Member] | Community Banking [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	79	34,314
Non-performing Loans and Leases [Member] | Community Banking [Member] | Commercial Operating [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	0
Total loans receivable	0	0
Non-performing Loans and Leases [Member] | Community Banking [Member] | Commercial Operating [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	0
Non-performing Loans and Leases [Member] | Community Banking [Member] | Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	0
Total loans receivable	0	19
Non-performing Loans and Leases [Member] | Community Banking [Member] | Consumer [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	19
Non-performing Loans and Leases [Member] | Community Banking [Member] | Commercial and Multi-Family Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	685
Total loans receivable	0	685
Non-performing Loans and Leases [Member] | Community Banking [Member] | Commercial and Multi-Family Real Estate [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	0
Non-performing Loans and Leases [Member] | Community Banking [Member] | 1-4 Family Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	0
Total loans receivable	79	0
Non-performing Loans and Leases [Member] | Community Banking [Member] | 1-4 Family Real Estate [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	79	0
Non-performing Loans and Leases [Member] | Community Banking [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	0	0
Total loans receivable	0	34,295
Non-performing Loans and Leases [Member] | Community Banking [Member] | Agricultural [Member] | Greater Than 90 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 0	$ 34,295