SECURITIES - Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022
Available-for-sale debt securities [Abstract]
Amortized Cost	$ 2,075,257	$ 2,165,719
Fair Value	1,825,563	1,882,869
Amortized Cost
Due in one year or less	3,785	718
Due after one year through five years	5,830	9,921
Due after five years through ten years	86,540	89,921
Due after ten years	444,746	483,707
Total	540,901	584,267
Mortgage-backed securities	1,534,356	1,581,452
Fair Value
Due in one year or less	3,728	715
Due after one year through five years	5,468	9,395
Due after five years through ten years	76,745	81,819
Due after ten years	405,611	441,943
Total	491,552	533,872
Mortgage-backed securities	1,334,011	1,348,997
Corporate securities
Available-for-sale debt securities [Abstract]
Amortized Cost	25,000	25,000
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(6,250)	(2,813)
Fair Value	18,750	22,187
LESS THAN 12 MONTHS, Fair Value	0	0
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	0	0
OVER 12 MONTHS, Fair Value	18,750	22,187
OVER 12 MONTHS, Gross Unrealized (Losses)	(6,250)	(2,813)
TOTAL, Fair Value	18,750	22,187
TOTAL, Gross Unrealized (Losses)	(6,250)	(2,813)
SBA securities
Available-for-sale debt securities [Abstract]
Amortized Cost	99,670	105,238
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(5,422)	(7,470)
Fair Value	94,248	97,768
LESS THAN 12 MONTHS, Fair Value	41,231	97,767
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	(1,166)	(7,470)
OVER 12 MONTHS, Fair Value	53,016	0
OVER 12 MONTHS, Gross Unrealized (Losses)	(4,256)	0
TOTAL, Fair Value	94,247	97,767
TOTAL, Gross Unrealized (Losses)	(5,422)	(7,470)
Obligations of states and political subdivisions
Available-for-sale debt securities [Abstract]
Amortized Cost	2,436	2,469
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(79)	(125)
Fair Value	2,357	2,344
LESS THAN 12 MONTHS, Fair Value	0	2,345
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	0	(125)
OVER 12 MONTHS, Fair Value	2,357	0
OVER 12 MONTHS, Gross Unrealized (Losses)	(79)	0
TOTAL, Fair Value	2,357	2,345
TOTAL, Gross Unrealized (Losses)	(79)	(125)
Non-bank qualified obligations of states and political subdivisions
Available-for-sale debt securities [Abstract]
Amortized Cost	277,767	290,754
Gross Unrealized Gains	37	0
Gross Unrealized (Losses)	(28,311)	(26,971)
Fair Value	249,493	263,783
LESS THAN 12 MONTHS, Fair Value	65,300	195,816
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	(4,118)	(19,743)
OVER 12 MONTHS, Fair Value	183,201	67,967
OVER 12 MONTHS, Gross Unrealized (Losses)	(24,193)	(7,228)
TOTAL, Fair Value	248,501	263,783
TOTAL, Gross Unrealized (Losses)	(28,311)	(26,971)
Asset-backed securities
Available-for-sale debt securities [Abstract]
Amortized Cost	136,028	160,806
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(9,324)	(13,016)
Fair Value	126,704	147,790
LESS THAN 12 MONTHS, Fair Value	0	64,886
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	0	(1,838)
OVER 12 MONTHS, Fair Value	126,704	82,904
OVER 12 MONTHS, Gross Unrealized (Losses)	(9,324)	(11,178)
TOTAL, Fair Value	126,704	147,790
TOTAL, Gross Unrealized (Losses)	(9,324)	(13,016)
Mortgage-backed securities
Available-for-sale debt securities [Abstract]
Amortized Cost	1,534,356	1,581,452
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(200,345)	(232,455)
Fair Value	1,334,011	1,348,997
LESS THAN 12 MONTHS, Fair Value	296,523	816,657
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	(14,199)	(106,583)
OVER 12 MONTHS, Fair Value	1,037,488	532,340
OVER 12 MONTHS, Gross Unrealized (Losses)	(186,146)	(125,872)
TOTAL, Fair Value	1,334,011	1,348,997
TOTAL, Gross Unrealized (Losses)	(200,345)	(232,455)
Total debt securities AFS
Available-for-sale debt securities [Abstract]
Amortized Cost	2,075,257	2,165,719
Gross Unrealized Gains	37	0
Gross Unrealized (Losses)	(249,731)	(282,850)
Fair Value	1,825,563	1,882,869
LESS THAN 12 MONTHS, Fair Value	403,054	1,177,471
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	(19,483)	(135,759)
OVER 12 MONTHS, Fair Value	1,421,516	705,398
OVER 12 MONTHS, Gross Unrealized (Losses)	(230,248)	(147,091)
TOTAL, Fair Value	1,824,570	1,882,869
TOTAL, Gross Unrealized (Losses)	$ (249,731)	$ (282,850)