FAIR VALUES OF FINANCIAL INSTRUMENTS - Assets Measured at Fair Value on Recurring and Non-recurring Basis (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between levels of fair value hierarchy	$ 0	$ 0
Available For Sale
Total debt securities	364,065,000	586,454,000
Total securities	1,852,025,000	1,693,431,000
Held To Maturity
Total securities	160,974,000	564,185,000
Fair value of assets measured on non-recurring basis [Abstract]
Foreclosed real estate and repossessed assets	31,638,000	292,000
Level 1 [Member]
Available For Sale
Total securities	3,800,000	1,445,000
Held To Maturity
Total securities	0	0
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
Level 2 [Member]
Available For Sale
Total securities	1,848,225,000	1,691,986,000
Held To Maturity
Total securities	160,974,000	564,185,000
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
Level 3 [Member]
Available For Sale
Total securities	0	0
Held To Maturity
Total securities	0	0
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	2,927,755,000	1,318,402,000
Recurring [Member]
Available For Sale
Small business administration securities	44,337,000	57,871,000
Obligations of states and political subdivisions	16,910,000	0
Non-bank qualified obligations of states and political subdivisions	1,109,885,000	950,829,000
Asset backed securities	313,028,000	96,832,000
Mortgage-backed securities	364,065,000	586,454,000
Total debt securities	1,848,225,000	1,691,986,000
Common Equities and Mutual Funds, Available-for-Sale	3,800,000	1,445,000
Total securities	1,852,025,000	1,693,431,000
Held To Maturity
Small business administration securities	0	0
Obligations of states and political subdivisions	0	19,368,000
Non-bank qualified obligations of states and political subdivisions	153,546,000	432,361,000
Asset backed securities	0	0
Mortgage-backed securities	7,428,000	112,456,000
Total debt securities	160,974,000	564,185,000
Common equities and mutual funds	0	0
Total securities	160,974,000	564,185,000
Recurring [Member] | Level 1 [Member]
Available For Sale
Small business administration securities	0	0
Obligations of states and political subdivisions	0	0
Non-bank qualified obligations of states and political subdivisions	0	0
Asset backed securities	0	0
Mortgage-backed securities	0	0
Total debt securities	0	0
Common Equities and Mutual Funds, Available-for-Sale	3,800,000	1,445,000
Total securities	3,800,000	1,445,000
Held To Maturity
Small business administration securities	0	0
Obligations of states and political subdivisions	0	0
Non-bank qualified obligations of states and political subdivisions	0	0
Asset backed securities	0	0
Mortgage-backed securities	0	0
Total debt securities	0	0
Common equities and mutual funds	0	0
Total securities	0	0
Recurring [Member] | Level 2 [Member]
Available For Sale
Small business administration securities	44,337,000	57,871,000
Obligations of states and political subdivisions	16,910,000	0
Non-bank qualified obligations of states and political subdivisions	1,109,885,000	950,829,000
Asset backed securities	313,028,000	96,832,000
Mortgage-backed securities	364,065,000	586,454,000
Total debt securities	1,848,225,000	1,691,986,000
Common Equities and Mutual Funds, Available-for-Sale	0	0
Total securities	1,848,225,000	1,691,986,000
Held To Maturity
Small business administration securities	0	0
Obligations of states and political subdivisions	0	19,368,000
Non-bank qualified obligations of states and political subdivisions	153,546,000	432,361,000
Asset backed securities	0	0
Mortgage-backed securities	7,428,000	112,456,000
Total debt securities	160,974,000	564,185,000
Common equities and mutual funds	0	0
Total securities	160,974,000	564,185,000
Recurring [Member] | Level 3 [Member]
Available For Sale
Small business administration securities	0	0
Obligations of states and political subdivisions	0	0
Non-bank qualified obligations of states and political subdivisions	0	0
Asset backed securities	0	0
Mortgage-backed securities	0	0
Total debt securities	0	0
Common Equities and Mutual Funds, Available-for-Sale	0	0
Total securities	0	0
Held To Maturity
Small business administration securities	0	0
Obligations of states and political subdivisions	0	0
Non-bank qualified obligations of states and political subdivisions	0	0
Asset backed securities	0	0
Mortgage-backed securities	0	0
Total debt securities	0	0
Common equities and mutual funds	0	0
Total securities	0	0
Nonrecurring [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Total	36,463,000	292,000
Nonrecurring [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	4,825,000
Nonrecurring [Member] | Foreclosed Assets, Net [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Foreclosed real estate and repossessed assets	31,638,000	292,000
Nonrecurring [Member] | Level 1 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Total	0	0
Nonrecurring [Member] | Level 1 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0
Nonrecurring [Member] | Level 1 [Member] | Foreclosed Assets, Net [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Foreclosed real estate and repossessed assets	0	0
Nonrecurring [Member] | Level 2 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Total	0	0
Nonrecurring [Member] | Level 2 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0
Nonrecurring [Member] | Level 2 [Member] | Foreclosed Assets, Net [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Foreclosed real estate and repossessed assets	0	0
Nonrecurring [Member] | Level 3 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Total	36,463,000	292,000
Nonrecurring [Member] | Level 3 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	4,825,000
Nonrecurring [Member] | Level 3 [Member] | Foreclosed Assets, Net [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Foreclosed real estate and repossessed assets	31,638,000	292,000
Community Banking [Member] | Level 1 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
Community Banking [Member] | Level 1 [Member] | 1-4 Family Real Estate [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
Community Banking [Member] | Level 1 [Member] | Commercial and Multi-Family Real Estate [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
Community Banking [Member] | Level 2 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
Community Banking [Member] | Level 2 [Member] | 1-4 Family Real Estate [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
Community Banking [Member] | Level 2 [Member] | Commercial and Multi-Family Real Estate [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
Community Banking [Member] | Level 3 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	1,076,782,000	920,439,000
Community Banking [Member] | Level 3 [Member] | 1-4 Family Real Estate [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	220,697,000	196,970,000
Community Banking [Member] | Level 3 [Member] | Commercial and Multi-Family Real Estate [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	731,291,000	576,330,000
Community Banking [Member] | Nonrecurring [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	4,825,000
Community Banking [Member] | Nonrecurring [Member] | Level 1 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0
Community Banking [Member] | Nonrecurring [Member] | Level 2 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0
Community Banking [Member] | Nonrecurring [Member] | Level 3 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	4,825,000
National Lending [Member] | Level 1 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
National Lending [Member] | Level 2 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0	0
National Lending [Member] | Level 3 [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	1,850,973,000	$ 397,963,000
National Lending [Member] | Nonrecurring [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	4,825,000
National Lending [Member] | Nonrecurring [Member] | Level 1 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0
National Lending [Member] | Nonrecurring [Member] | Level 2 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	0
National Lending [Member] | Nonrecurring [Member] | Level 3 [Member] | Total Impaired Loans [Member]
Fair value of assets measured on non-recurring basis [Abstract]
Impaired Loans, Net	$ 4,825,000