Securities (Amortized Cost, Estimated Fair Value, and Gross Unrealized Gains and Losses of AFS and HTM Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost	$ 829,852	$ 1,385,992
Available-for-sale Securities, Gross Unrealized Gains	27,113	113
Available-for-sale Securities, Gross Unrealized Losses	699	1,623
Available-for-sale Securities, Estimated Fair Value	856,266	1,384,482
MBS [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost	756,775
Available-for-sale Securities, Gross Unrealized Gains	26,885
Available-for-sale Securities, Gross Unrealized Losses	87
Available-for-sale Securities, Estimated Fair Value	783,573
Residential MBS [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost		901,440
Available-for-sale Securities, Gross Unrealized Gains		113
Available-for-sale Securities, Gross Unrealized Losses		819
Available-for-sale Securities, Estimated Fair Value	713,300	900,734
GSE Debentures [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost	69,077	479,610
Available-for-sale Securities, Gross Unrealized Gains	228	0
Available-for-sale Securities, Gross Unrealized Losses	0	182
Available-for-sale Securities, Estimated Fair Value	69,305	479,428
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost	4,000	4,000
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	612	622
Available-for-sale Securities, Estimated Fair Value	$ 3,388	3,378
Municipal Bonds [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost		942
Available-for-sale Securities, Gross Unrealized Gains		0
Available-for-sale Securities, Gross Unrealized Losses		0
Available-for-sale Securities, Estimated Fair Value		$ 942

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

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Amortized cost excluding accrued interest, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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