Regulatory Matters: Schedule of Compliance with Regulatory Capital Requirements for Mortgage Companies (Details) $ in Thousands	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Timberland Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Leverage Capital, Actual Amount	$ 229,206	$ 218,749
Tier 1 Leverage Capital, Actual Ratio	0.120	0.120
Tier 1 Leverage Capital, Regulatory Minimum To Be Adequately Capitalized, Amount	$ 76,319	$ 72,983
Tier 1 Leverage Capital, Regulatory Minimum To Be Adequately Capitalized, Ratio	0.040	0.040
Tier 1 Leverage Capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 95,399	$ 91,229
Tier 1 Leverage Capital, To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.050	0.050
Tier 1 Risk-based Capital Ratio, Common Equity, Actual Amount	$ 229,206	$ 218,749
Tier 1 Risk-based Capital Ratio, Common Equity, Actual Ratio	18.00%	18.00%
Tier 1 Risk-based Capital Ratio, Regulatory Minimum To Be Adequately Capitalized, Amount	$ 57,318	$ 54,549
Tier 1 Risk-based Capital Ratio, Regulatory Minimum To Be Adequately Capitalized, Ratio	4.50%	4.50%
Tier 1 Risk-based Capital Ratio, Regulatory Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 82,793	$ 78,792
Tier 1 Risk-based Capital Ratio, Regulatory Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Tier 1 Risk-based Capital, Actual Amount	$ 229,206	$ 218,749
Tier 1 Risk-based Capital, Actual Ratio	0.180	0.180
Tier 1 Risk-based Capital, Regulatory Minimum To Be Adequately Capitalized, Amount	$ 76,424	$ 72,731
Tier 1 Risk-based Capital, Regulatory Minimum To Be Adequately Capitalized, Ratio	0.060	0.060
Tier 1 Risk-based Capital, Regulatory Minimum To Be Well Capitalized, Amount	$ 101,899	$ 96,975
Tier 1 Risk-based Capital, Regulatory Minimum To Be Well Capitalized, Ratio	0.080	0.080
Total Capital, Actual Amount	$ 245,152	$ 233,914
Total Capital, Actual Ratio	0.193	0.193
Total Capital, Regulatory Minimum To Be Adequately Capitalized, Amount	$ 101,899	$ 96,975
Total Capital, Regulatory Minimum To Be Adequately Capitalized, Ratio	0.080	0.080
Total Capital, Regulatory Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 127,374	$ 121,219
Total Capital, Regulatory Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.100	0.100
Timberland Bancorp
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 Leverage Capital, Actual Amount	$ 231,092	$ 219,851
Tier 1 Leverage Capital, Actual Ratio	0.121	0.121
Tier 1 Risk-based Capital Ratio, Common Equity, Actual Amount	$ 231,092	$ 219,851
Tier 1 Risk-based Capital Ratio, Common Equity, Actual Ratio	18.10%	18.10%
Tier 1 Risk-based Capital, Actual Amount	$ 231,092	$ 219,851
Tier 1 Risk-based Capital, Actual Ratio	0.181	0.181
Total Capital, Actual Amount	$ 247,044	$ 235,023
Total Capital, Actual Ratio	0.194	0.194

Tier One Risk Adjusted Capital

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Amount of minimum total risk-based capital required for capital adequacy as defined by regulatory framework.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1

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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.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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