FAIR VALUE OF FINANCIAL INSTRUMENTS - Assets Measured at Fair Value on Recurring and Non-recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Level 1
Available-for-sale debt securities [Abstract]
Total debt securities AFS	$ 0	$ 0
Common equities and mutual funds	3,065	12,668
Level 2
Available-for-sale debt securities [Abstract]
Total debt securities AFS	1,956,523	1,864,899
Common equities and mutual funds	0	0
Level 3
Available-for-sale debt securities [Abstract]
Total debt securities AFS	0	0
Common equities and mutual funds	0	0
Recurring
Available-for-sale debt securities [Abstract]
Corporate securities	23,438	25,000
SBA securities	81,349	157,209
Obligations of states and political subdivisions	2,641	2,507
Non-bank qualified obligations of states and political subdivisions	244,961	268,295
Asset-backed securities	159,332	394,859
Mortgage-backed securities	1,444,802	1,017,029
Total debt securities AFS	1,956,523	1,864,899
Common equities and mutual funds	3,065	12,668
Non-marketable equity securities	6,494	4,560
Recurring \| Level 1
Available-for-sale debt securities [Abstract]
Corporate securities	0	0
SBA 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 AFS	0	0
Common equities and mutual funds	3,065	12,668
Non-marketable equity securities	0	0
Recurring \| Level 2
Available-for-sale debt securities [Abstract]
Corporate securities	23,438	25,000
SBA securities	81,349	157,209
Obligations of states and political subdivisions	2,641	2,507
Non-bank qualified obligations of states and political subdivisions	244,961	268,295
Asset-backed securities	159,332	394,859
Mortgage-backed securities	1,444,802	1,017,029
Total debt securities AFS	1,956,523	1,864,899
Common equities and mutual funds	0	0
Non-marketable equity securities	0	0
Recurring \| Level 3
Available-for-sale debt securities [Abstract]
Corporate securities	0	0
SBA 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 AFS	0	0
Common equities and mutual funds	0	0
Non-marketable equity securities	$ 0	$ 0

Fair value of asset backed securities investments classified as available for sale.

No definition available.

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Balance Type:	debit
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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents common equities and mutual funds as of the balance sheet date which have been categorized as available-for-sale.

+ References

No definition available.

+ Details

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- Definition

Corporate Securities Available For Sale

+ References

No definition available.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents non-bank qualified obligations of states and political subdivision as of the balance sheet date which have been categorized as available-for-sale.

+ References

No definition available.

+ Details

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents obligations of states and political subdivision as of the balance sheet date which have been categorized as available-for-sale.

+ References

No definition available.

+ Details

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents debt securities issued by the Small Business Administration (SBA) as of the balance sheet date which have been categorized as available-for-sale.

+ References

No definition available.

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- References

No definition available.

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
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-Name Accounting Standards Codification
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Namespace Prefix:	us-gaap_
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Balance Type:	debit
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- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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-Name Accounting Standards Codification
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-Name Accounting Standards Codification
-Topic 825
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-URI https://asc.fasb.org/extlink&oid=123594786&loc=SL75136599-209740

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Balance Type:	debit
Period Type:	instant

- Definition

Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as available-for-sale.

+ References

No definition available.

+ Details

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