Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023
Other assets
Derivatives, Fair Value [Line Items]
Notional amount	$ 2,903,527	$ 2,516,405
Derivative assets, fair value	223,782	312,971
Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	896,485	806,744
Derivative liabilities, fair value	56,392	79,668
Client swap program hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional amount	896,485	806,744
Derivative assets, fair value	55,631	78,797
Client swap program hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	896,485	806,744
Derivative liabilities, fair value	56,392	79,668
Commercial loan fair value hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional amount	37,042	39,661
Derivative assets, fair value	2,061	3,405
Commercial loan fair value hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	0	0
Derivative liabilities, fair value	0	0
Mortgage loan fair value hedges
Derivatives, Fair Value [Line Items]
Notional amount	970,000	670,000
Mortgage loan fair value hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional amount	970,000
Derivative assets, fair value	22,244	46,396
Mortgage loan fair value hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	0	0
Derivative liabilities, fair value	0	0
Borrowings cash flow hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional amount	1,000,000	1,000,000
Derivative assets, fair value	143,846	184,373
Borrowings cash flow hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	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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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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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.

+ References

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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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No definition available.

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