SECURITIES - Narrative (Details)	12 Months Ended
	Sep. 30, 2024 USD ($) security	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Debt Securities, Available-for-sale [Line Items]
Number of securities in an unrealized loss position | security	195
Securities pledged as collateral for public funds on deposit	$ 0	$ 0
Securities pledged as collateral for individual, trust, and estate deposits	0	0
Federal reserve bank stock	19,700,000	19,700,000
Federal Reserve Bank and Federal Home Loan Bank Stock, at cost	16,300,000	8,500,000
Loans	4,029,859,000	4,316,411,000
Determinable fair value	13,600,000	16,200,000
Impairment recognized	1,000,000.0	3,300,000	$ 0
Estimated Fair Value
Debt Securities, Available-for-sale [Line Items]
Loans and leases	4,036,490,000	4,223,010,000
Marketable
Debt Securities, Available-for-sale [Line Items]
Equity securities	3,300,000	3,400,000
Unrealized loss	100,000	200,000
Non-marketable
Debt Securities, Available-for-sale [Line Items]
Equity securities	11,800,000	8,400,000
Unrealized gains on marketable equity securities	(1,100,000)	200,000
Realized gains on marketable equity securities	$ 2,500,000
Number of equity securities sold | security	1
Non-marketable | Visa Class C Common Stock and Visa Class B-2 Common Stock
Debt Securities, Available-for-sale [Line Items]
Realized gains on marketable equity securities	$ 2,400,000
Asset Pledged as Collateral with Right | Estimated Fair Value | Federal Home Loan Bank Advances
Debt Securities, Available-for-sale [Line Items]
Loans and leases	1,040,000,000.00	996,900,000
Asset Pledged as Collateral
Debt Securities, Available-for-sale [Line Items]
Investments	533,800,000	773,600,000
Loans	136,900,000	21,300,000
Federal Reserve Bank
Debt Securities, Available-for-sale [Line Items]
Interest and dividend income from FLHB	1,200,000	1,200,000	1,200,000
Federal Home Loan Bank
Debt Securities, Available-for-sale [Line Items]
Interest and dividend income from FLHB	$ 700,000	$ 500,000	$ 300,000