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Derivatives and Hedging Activities - Gains/(Losses) on Derivative Instruments in Fair Value and Cash Flow Accounting Hedging Relationships (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Interest income/(expense), including the effects of fair value and cash flow hedges | $ 601,592 | $ 537,660 | $ 545,708
Interest income/(expense), including the effects of fair value and cash flow hedges | (28,729) | (44,188) | $ (51,445)
Gain/(loss) on cash flow hedging relationships: |  |  |
Gain (loss) recognized on cash flow hedges | 0 | 0 |
Interest rate contracts | Interest income on loans receivable | Fair value hedging |  |  |
Gain/(loss) on fair value hedging relationships: |  |  |
Amounts related to interest settlements on derivatives | (1,782) | (6,320) |
Recognized on derivatives | 43,100 | 20,736 |
Recognized on hedged items | (43,305) | (20,449) |
Net income/(expense) recognized on fair value hedges | (1,987) | (6,033) |
Interest rate contracts | Interest expense on FHLB advances | Cash flow hedging |  |  |
Gain/(loss) on cash flow hedging relationships: |  |  |
Amounts related to interest settlements on derivatives | (408) | 10,846 |
Amount of derivative gain/(loss) reclassified from AOCI into interest income/expense | 0 | 14,110 |
Gain (loss) recognized on cash flow hedges | $ (408) | $ 24,956 |

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- Definition Amount of gain (loss) from the increase (decrease) in fair value of derivative and nonderivative instruments designated as fair value hedging instruments recognized in the income statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI https://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986 + Details
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- Definition Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI https://asc.fasb.org/extlink&oid=121577467&loc=d3e76258-113986 + Details
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- Definition Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624171-113959 + Details
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- Definition The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.1) -URI https://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260 + Details
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