Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Other assets
Derivatives, Fair Value [Line Items]
Notional	$ 1,981,554	$ 2,516,405
Derivative assets, fair value	165,624	312,971
Other liabilities
Derivatives, Fair Value [Line Items]
Notional	3,614,512	806,744
Derivative liabilities, fair value	48,055	79,668
Client swap program hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional	1,044,512	806,744
Derivative assets, fair value	46,758	78,797
Client swap program hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional	1,044,512	806,744
Derivative liabilities, fair value	47,388	79,668
Commercial loan fair value hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional	37,042	39,661
Derivative assets, fair value	1,595	3,405
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	0
Derivative assets, fair value	0	46,396
Mortgage loan fair value hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional	2,570,000	0
Derivative liabilities, fair value	667	0
Borrowings cash flow hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional	900,000	1,000,000
Derivative assets, fair value	117,271	184,373
Borrowings cash flow hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional	0	0
Derivative liabilities, fair value	$ 0	$ 0

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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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or 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 liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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- Definition

Nominal or face amount used to calculate payment on derivative.

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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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