Securities (Amortized Cost, Estimated Fair Value, and Gross Unrealized Gains and Losses of AFS and HTM Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Sep. 30, 2024
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost	$ 933,360	$ 829,852
Available-for-sale Securities, Gross Unrealized Gains	23,531	27,113
Available-for-sale Securities, Gross Unrealized Losses	662	699
Available-for-sale Securities, Estimated Fair Value	956,229	856,266
MBS [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost	874,360	756,775
Available-for-sale Securities, Gross Unrealized Gains	23,527	26,885
Available-for-sale Securities, Gross Unrealized Losses	312	87
Available-for-sale Securities, Estimated Fair Value	897,575	783,573
GSE Debentures [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Amortized Cost	55,000	69,077
Available-for-sale Securities, Gross Unrealized Gains	4	228
Available-for-sale Securities, Gross Unrealized Losses	49	0
Available-for-sale Securities, Estimated Fair Value	54,955	69,305
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	301	612
Available-for-sale Securities, Estimated Fair Value	$ 3,699	$ 3,388

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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- Definition

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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- Definition

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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