Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Other assets
Derivatives, Fair Value [Line Items]
Notional	$ 2,516,405	$ 2,100,885
Derivative assets, fair value	312,971	286,487
Other liabilities
Derivatives, Fair Value [Line Items]
Notional	806,744	588,676
Derivative liabilities, fair value	79,668	67,260
Client swap program hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional	806,744	588,676
Derivative assets, fair value	78,797	67,260
Client swap program hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional	806,744	588,676
Derivative liabilities, fair value	79,668	67,260
Commercial loan fair value hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional	39,661	42,209
Derivative assets, fair value	3,405	2,517
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	670,000	470,000
Derivative assets, fair value	46,396	36,765
Mortgage loan fair value hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional	0	0
Derivative liabilities, fair value	0	0
Borrowings cash flow hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional	1,000,000	1,000,000
Derivative assets, fair value	184,373	179,945
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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