FAIR VALUES OF FINANCIAL INSTRUMENTS - Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Sep. 30, 2021
Financial assets
Debt securities held to maturity	$ 38,171	$ 56,391
Level 1
Financial assets
Cash and cash equivalents	388,038	314,019
Debt securities available for sale	0	0
Debt securities held to maturity	0	0
Common equities and mutual funds	2,874	12,668
Non-marketable equity securities	0	0
Loans held for sale	0	0
Loans and leases	0	0
Federal Reserve Bank and Federal Home Loan Bank stocks	0	0
Accrued interest receivable	17,979	16,254
Financial liabilities
Deposits	5,858,283	5,482,471
Other short- and long-term borrowings	0	0
Accrued interest payable	192	579
Level 2
Financial assets
Cash and cash equivalents	0	0
Debt securities available for sale	1,882,869	1,864,899
Debt securities held to maturity	38,171	56,391
Common equities and mutual funds	0	0
Non-marketable equity securities	15,314	12,949
Loans held for sale	21,071	56,194
Loans and leases	0	0
Federal Reserve Bank and Federal Home Loan Bank stocks	28,812	28,400
Accrued interest receivable	0	0
Financial liabilities
Deposits	7,571	32,564
Other short- and long-term borrowings	35,986	93,938
Accrued interest payable	0	0
Level 3
Financial assets
Cash and cash equivalents	0	0
Debt securities available for sale	0	0
Debt securities held to maturity	0	0
Common equities and mutual funds	0	0
Non-marketable equity securities	0	0
Loans held for sale	0	0
Loans and leases	3,525,803	3,616,646
Federal Reserve Bank and Federal Home Loan Bank stocks	0	0
Accrued interest receivable	0	0
Financial liabilities
Deposits	0	0
Other short- and long-term borrowings	0	0
Accrued interest payable	0	0
Carrying Amount
Financial assets
Cash and cash equivalents	388,038	314,019
Debt securities available for sale	1,882,869	1,864,899
Debt securities held to maturity	41,682	56,669
Common equities and mutual funds	2,874	12,668
Non-marketable equity securities	22,526	17,509
Loans held for sale	21,071	56,194
Loans and leases	3,529,280	3,607,815
Federal Reserve Bank and Federal Home Loan Bank stocks	28,812	28,400
Accrued interest receivable	17,979	16,254
Financial liabilities
Deposits	5,866,037	5,514,971
Other short- and long-term borrowings	36,028	92,834
Accrued interest payable	192	579
Estimated Fair Value
Financial assets
Cash and cash equivalents	388,038	314,019
Debt securities available for sale	1,882,869	1,864,899
Debt securities held to maturity	38,171	56,391
Common equities and mutual funds	2,874	12,668
Non-marketable equity securities	22,526	17,509
Loans held for sale	21,071	56,194
Loans and leases	3,525,803	3,616,646
Federal Reserve Bank and Federal Home Loan Bank stocks	28,812	28,400
Accrued interest receivable	17,979	16,254
Financial liabilities
Deposits	5,865,854	5,515,035
Other short- and long-term borrowings	35,986	93,938
Accrued interest payable	$ 192	$ 579