Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Other assets
Derivatives, Fair Value [Line Items]
Notional amount	$ 526,301	$ 625,607
Derivative assets, fair value	47,972	21,989
Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	2,719,617	1,221,252
Derivative liabilities, fair value	99,902	32,546
Client swap program hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional amount	526,301	425,607
Derivative assets, fair value	47,972	20,381
Client swap program hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	526,301	425,607
Derivative liabilities, fair value	47,972	20,381
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	93,316	95,645
Derivative liabilities, fair value	9,090	4,288
Mortgage loan fair value hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional amount	0	200,000
Derivative assets, fair value	0	1,608
Mortgage loan fair value hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	500,000	0
Derivative liabilities, fair value	17,605	0
Borrowings cash flow hedges \| Other assets
Derivatives, Fair Value [Line Items]
Notional amount	0	0
Derivative assets, fair value	0	0
Borrowings cash flow hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional amount	1,600,000	700,000
Derivative liabilities, fair value	$ 25,235	$ 7,877

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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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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