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DERIVATIVES AND HEDGING ACTIVITIES - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Other assets
Derivatives, Fair Value [Line Items]
Notional	$ 2,381,358	$ 1,981,554
Derivative assets, fair value	151,271	165,624
Other liabilities
Derivatives, Fair Value [Line Items]
Notional	2,687,017	3,614,512
Derivative liabilities, fair value	73,330	48,055
Client swap program hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional	977,017	1,044,512
Derivative assets, fair value	37,347	46,758
Client swap program hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional	977,017	1,044,512
Derivative liabilities, fair value	37,818	47,388
Commercial loan fair value hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional	34,341	37,042
Derivative assets, fair value	1,611	1,595
Commercial loan fair value hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional	0	0
Derivative liabilities, fair value	0	0
Mortgage loan fair value hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional	470,000	0
Derivative assets, fair value	13,082	0
Mortgage loan fair value hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional	1,100,000	2,570,000
Derivative liabilities, fair value	20,426	667
Mortgage backed securities fair value hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional	0
Derivative assets, fair value	0
Mortgage backed securities fair value hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional	610,000
Derivative liabilities, fair value	15,086
Borrowings cash flow hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional	900,000	900,000
Derivative assets, fair value	99,231	117,271
Borrowings cash flow hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional	0	0
Derivative liabilities, fair value	$ 0	$ 0

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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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