DERIVATIVES AND HEDGING ACTIVITIES - Impact of Fair Value Hedge Accounting on the Carrying Value of the Hedged Items (Details) - USD ($)	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024
Derivatives, Fair Value [Line Items]
Carrying value of hedged items	$ 6,366,196,000	$ 7,287,540,000
Hedged Liability, Statement of Financial Position [Extensible Enumeration]		Loans receivable, net of allowance for loan losses of $199,720 and $203,753
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items	22,246,000	$ 20,005,000
Mortgage loan fair value hedges
Derivatives, Fair Value [Line Items]
Portfolio layer method, amortized cost	5,393,257,000	7,252,017,000
Portfolio layer method, cumulative adjustment, increase (decrease)	8,262,000	21,476,000
Amortized cost, designated in portfolio hedging relationship	1,570,000,000	2,570,000,000
Hedged asset, discontinued	1,600,000,000	300,000,000
Hedged asset, discontinued fair value	4,016,668	1,232,211
Commercial loan fair value hedges
Derivatives, Fair Value [Line Items]
Carrying value of hedged items	32,829,000	35,523,000
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items	(1,468,000)	$ (1,471,000)
Mortgage backed securities fair value hedges
Derivatives, Fair Value [Line Items]
Carrying value of hedged items	940,110,000
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items	15,452,000
Amortized cost, designated in portfolio hedging relationship	610,000,000
Loans receivable
Derivatives, Fair Value [Line Items]
Carrying value of hedged items	$ 5,426,086,000
Hedged Liability, Statement of Financial Position [Extensible Enumeration]	Loans receivable, net of allowance for loan losses of $199,720 and $203,753
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items	$ 6,794,000
Available-for-sale Securities LOL
Derivatives, Fair Value [Line Items]
Carrying value of hedged items	$ 940,110,000
Hedged Liability, Statement of Financial Position [Extensible Enumeration]	Available-for-sale securities, at fair value
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items	$ 15,452,000

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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