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Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($) $ in Thousands | Dec. 31, 2022 | Sep. 30, 2022
--- | --- | ---
Other assets |  |
Derivatives, Fair Value [Line Items] |  |
Notional amount | $ 2,093,443 | $ 2,100,885
Derivative assets, fair value | 272,955 | 286,487
Other liabilities |  |
Derivatives, Fair Value [Line Items] |  |
Notional amount | 583,782 | 588,676
Derivative liabilities, fair value | 63,383 | 67,260
Client swap program hedges | Other assets |  |
Derivatives, Fair Value [Line Items] |  |
Notional amount | 583,782 | 588,676
Derivative assets, fair value | 63,383 | 67,260
Client swap program hedges | Other liabilities |  |
Derivatives, Fair Value [Line Items] |  |
Notional amount | 583,782 | 588,676
Derivative liabilities, fair value | 63,383 | 67,260
Commercial loan fair value hedges | Other assets |  |
Derivatives, Fair Value [Line Items] |  |
Notional amount | 39,661 | 42,209
Derivative assets, fair value | 2,447 | 2,517
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 | 470,000 |
Mortgage loan fair value hedges | Other assets |  |
Derivatives, Fair Value [Line Items] |  |
Notional amount | 470,000 | 470,000
Derivative assets, fair value | 33,986 | 36,765
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 | 173,139 | 179,945
Borrowings cash flow hedges | Other liabilities |  |
Derivatives, Fair Value [Line Items] |  |
Notional amount | 0 | 0
Derivative liabilities, fair value | $ 0 | $ 0

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- 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. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 22 -URI https://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 7 -URI https://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 4D -Subparagraph (c)(2) -URI https://asc.fasb.org/extlink&oid=121570589&loc=SL51823488-111719 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -Subparagraph (a),(c) -URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959 + Details
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