Derivatives and Hedging Activities - Impact of Fair Value Hedge Accounting on the Carrying Value of the Hedged Items (Details) - USD ($)	Sep. 30, 2022	Sep. 30, 2021
Loans receivable
Derivatives, Fair Value [Line Items]
Carrying value of hedged items	$ 1,159,496,000	$ 1,515,487,000
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items	(39,090,000)	4,215,000
Other liabilities
Derivatives, Fair Value [Line Items]
Notional	588,676,000	1,159,033,000
Mortgage loan fair value hedges
Derivatives, Fair Value [Line Items]
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items	(36,458,000)	1,864,000
Hedged asset, discontinued fair value		$ 30,000,000
Hedged asset, discontinued fair value (percent)		3000.00%
Hedged asset, total last of layer hedge		$ 100,000,000
Unamortized discount, termination portion of hedge		1,238,000
Mortgage loan fair value hedges \| Loans receivable
Derivatives, Fair Value [Line Items]
Carrying value of hedged items	1,119,975,000
Hedged liability, amortized cost		1,468,517,000
Mortgage loan fair value hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional	0	470,000,000
Commercial loan fair value hedges
Derivatives, Fair Value [Line Items]
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items	(2,632,000)	2,351,000
Hedged asset, discontinued fair value		46,240,000
Commercial loan fair value hedges \| Loans receivable
Derivatives, Fair Value [Line Items]
Carrying value of hedged items	39,521,000	46,970,000
Commercial loan fair value hedges \| Other liabilities
Derivatives, Fair Value [Line Items]
Notional	$ 0	$ 44,678,000

Nominal or face amount used to calculate payment on derivative.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959

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Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk, remaining after discontinued hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL109999712-113959

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Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL109999712-113959

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- Definition

Amount of liability hedged in fair value hedging relationship.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL109999712-113959

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