v3.25.1

Investment Securities: Narrative (Details)	6 Months Ended
Investment Securities: Narrative (Details)	Mar. 31, 2025 USD ($) security	Mar. 31, 2024 USD ($)	Dec. 31, 2024 USD ($)	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)
Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Line Items]
Realized loss on marketable security	$ 2,000	$ 0
Held-to-maturity securities, realized loss, number of securities \| security	13
Security owned and pledged as collateral	$ 202,440,000			$ 208,810,000
Allowance for credit losses	50,000	85,000	$ 55,000	60,000	$ 82,000	$ 0
Accrued interest on held-to-maturity securites	635,000
Private label residential
Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Line Items]
Allowance for credit losses	48,000	$ 77,000	$ 52,000	$ 55,000	$ 73,000	$ 0
Held-to-maturity securities in non-accrual status	$ 41,000

Held-to-Maturity Securities, Gross Realized Loss, Number of Securities

+ References

No definition available.

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- Definition

Amount, before allowance for credit loss, of accrued interest on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

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- Definition

Amount, excluding accrued interest, of allowance for credit loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

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- Definition

Amount excluding accrued interest, of investment in debt security measured at amortized cost (held-to-maturity) on nonaccrual status.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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- Definition

The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 940
-SubTopic 320
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479035/940-320-45-2

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- Definition

Amount of realized gain (loss) on investment in marketable security.

+ References

No definition available.

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TIMBERLAND BANCORP INC 10-Q