SECURITIES - Available for Sale (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Available-for-sale debt securities [Abstract]
Amortized Cost	$ 1,782,201	$ 1,855,084
Fair Value	1,782,739	1,864,899
Amortized Cost
Due in one year or less	810	810
Due after one year through five years	13,009	13,026
Due after five years through ten years	76,762	50,785
Due after ten years	713,284	773,985
Total	803,865	838,606
Mortgage-backed securities	978,336	1,016,478
Fair Value
Due in one year or less	814	822
Due after one year through five years	13,245	13,378
Due after five years through ten years	77,893	52,357
Due after ten years	716,407	781,313
Total	808,359	847,870
Mortgage-backed securities	974,380	1,017,029
Corporate securities
Available-for-sale debt securities [Abstract]
Amortized Cost	25,000	25,000
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	0	0
Fair Value	25,000	25,000
SBA securities
Available-for-sale debt securities [Abstract]
Amortized Cost	146,639	151,958
Gross Unrealized Gains	4,200	5,251
Gross Unrealized (Losses)	0	0
Fair Value	150,839	157,209
Obligations of states and political subdivisions
Available-for-sale debt securities [Abstract]
Amortized Cost	2,793	2,497
Gross Unrealized Gains	6	10
Gross Unrealized (Losses)	0	0
Fair Value	2,799	2,507
Non-bank qualified obligations of states and political subdivisions
Available-for-sale debt securities [Abstract]
Amortized Cost	250,241	266,048
Gross Unrealized Gains	2,056	3,347
Gross Unrealized (Losses)	(1,425)	(1,100)
Fair Value	250,872	268,295
LESS THAN 12 MONTHS, Fair Value	110,535	101,046
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	(1,425)	(1,100)
OVER 12 MONTHS, Fair Value	0	0
OVER 12 MONTHS, Gross Unrealized (Losses)	0	0
TOTAL, Fair Value	110,535	101,046
TOTAL, Gross Unrealized (Losses)	(1,425)	(1,100)
Asset-backed securities
Available-for-sale debt securities [Abstract]
Amortized Cost	379,192	393,103
Gross Unrealized Gains	2,331	3,003
Gross Unrealized (Losses)	(2,674)	(1,247)
Fair Value	378,849	394,859
LESS THAN 12 MONTHS, Fair Value	198,807	127,110
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	(2,376)	(283)
OVER 12 MONTHS, Fair Value	46,215	91,553
OVER 12 MONTHS, Gross Unrealized (Losses)	(298)	(964)
TOTAL, Fair Value	245,022	218,663
TOTAL, Gross Unrealized (Losses)	(2,674)	(1,247)
Mortgage-backed securities
Available-for-sale debt securities [Abstract]
Amortized Cost	978,336	1,016,478
Gross Unrealized Gains	6,962	9,728
Gross Unrealized (Losses)	(10,918)	(9,177)
Fair Value	974,380	1,017,029
LESS THAN 12 MONTHS, Fair Value	702,224	759,035
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	(8,427)	(7,418)
OVER 12 MONTHS, Fair Value	90,298	60,792
OVER 12 MONTHS, Gross Unrealized (Losses)	(2,491)	(1,759)
TOTAL, Fair Value	792,522	819,827
TOTAL, Gross Unrealized (Losses)	(10,918)	(9,177)
Total debt securities AFS
Available-for-sale debt securities [Abstract]
Amortized Cost	1,782,201	1,855,084
Gross Unrealized Gains	15,555	21,339
Gross Unrealized (Losses)	(15,017)	(11,524)
Fair Value	1,782,739	1,864,899
LESS THAN 12 MONTHS, Fair Value	1,011,566	987,191
LESS THAN 12 MONTHS, Gross Unrealized (Losses)	(12,228)	(8,801)
OVER 12 MONTHS, Fair Value	136,513	152,345
OVER 12 MONTHS, Gross Unrealized (Losses)	(2,789)	(2,723)
TOTAL, Fair Value	1,148,079	1,139,536
TOTAL, Gross Unrealized (Losses)	$ (15,017)	$ (11,524)

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).