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Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Other assets
Derivatives, Fair Value [Line Items]
Notional amount	$ 2,103,056	$ 1,644,355
Derivative assets, fair value	57,464	53,425
Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	675,265	1,159,033
Derivative liabilities, fair value	7,895	14,801
Client swap program hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional amount	633,056	644,355
Derivative assets, fair value	5,944	10,983
Client swap program hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	633,056	644,355
Derivative liabilities, fair value	5,944	10,983
Commercial loan fair value hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional amount	0	0
Derivative assets, fair value	0	0
Commercial loan fair value hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	42,209	44,678
Derivative liabilities, fair value	1,951	2,177
Mortgage loan fair value hedges
Derivatives, Fair Value [Line Items]
Notional amount	470,000
Mortgage loan fair value hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional amount	470,000	0
Derivative assets, fair value	2,632	0
Mortgage loan fair value hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	0	470,000
Derivative liabilities, fair value	0	1,641
Borrowings cash flow hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional amount	1,000,000	1,000,000
Derivative assets, fair value	48,888	42,442
Borrowings cash flow hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	0	0
Derivative liabilities, fair value	$ 0	$ 0

X

- 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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X

- 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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