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Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Other assets
Derivatives, Fair Value [Line Items]
Notional amount	$ 2,137,633	$ 656,074
Derivative assets, fair value	38,568	48,201
Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	1,228,551	2,849,390
Derivative liabilities, fair value	55,792	90,129
Client swap program hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional amount	637,633	656,074
Derivative assets, fair value	35,825	48,201
Client swap program hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	637,633	656,074
Derivative liabilities, fair value	35,825	48,201
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	90,918	93,316
Derivative liabilities, fair value	7,508	8,492
Mortgage loan fair value hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional amount	0	0
Derivative assets, fair value	0	0
Mortgage loan fair value hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	500,000	500,000
Derivative liabilities, fair value	12,459	16,061
Borrowings cash flow hedges | Other assets
Derivatives, Fair Value [Line Items]
Notional amount	1,500,000	0
Derivative assets, fair value	2,743	0
Borrowings cash flow hedges | Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	0	1,600,000
Derivative liabilities, fair value	$ 0	$ 17,375

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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- 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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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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