Loans Receivable and Allowance for Loan Losses: Past Due Status of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	$ 1,487,209	$ 1,444,426
Non-accrual loans	4,407	3,885
Recorded Investment			$ 4,009
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	374	424
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	876	170
Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	5,657	4,479
Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	1,481,552	1,439,947
Mortgage loans, one-to-four family
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	317,691	299,123
Non-accrual loans	1,781	49
Recorded Investment			368
Mortgage loans, one-to-four family \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, one-to-four family \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	210	0
Mortgage loans, one-to-four family \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans, one-to-four family \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	1,991	49
Mortgage loans, one-to-four family \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	315,700	299,074
Mortgage loans, multi-family
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	207,767	177,350
Non-accrual loans	0	0
Mortgage loans, multi-family \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, multi-family \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, multi-family \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans, multi-family \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, multi-family \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	207,767	177,350
Mortgage loans, commercial
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	610,692	599,219
Non-accrual loans	159	1,158
Recorded Investment			2,973
Mortgage loans, commercial \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, commercial \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	255	0
Mortgage loans, commercial \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans, commercial \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	414	1,158
Mortgage loans, commercial \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	610,278	598,061
Mortgage loans, construction - custom and owner/builder
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	80,718	81,274
Non-accrual loans	553	0
Mortgage loans, construction - custom and owner/builder \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - custom and owner/builder \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - custom and owner/builder \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans, construction - custom and owner/builder \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	553	0
Mortgage loans, construction - custom and owner/builder \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	80,165	81,274
Mortgage loans, construction - speculative one-to-four family
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	6,923	7,451
Non-accrual loans	0	0
Mortgage loans, construction - speculative one-to-four family \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - speculative one-to-four family \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - speculative one-to-four family \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans, construction - speculative one-to-four family \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - speculative one-to-four family \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	6,923	7,451
Mortgage loans, construction - commercial
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	15,734	23,812
Non-accrual loans	0	0
Mortgage loans, construction - commercial \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - commercial \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - commercial \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans, construction - commercial \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - commercial \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	15,734	23,812
Mortgage loans, construction - multi-family
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	18,688	20,757
Non-accrual loans	0	0
Mortgage loans, construction - multi-family \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - multi-family \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - multi-family \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans, construction - multi-family \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, construction - multi-family \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	18,688	20,757
Mortgage loans - construction - land development
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	13,536	16,029
Non-accrual loans	0	0
Mortgage loans - construction - land development \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans - construction - land development \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans - construction - land development \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans - construction - land development \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans - construction - land development \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	13,536	16,029
Mortgage loans, land
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	35,952	29,366
Non-accrual loans	0	0
Recorded Investment			0
Mortgage loans, land \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, land \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, land \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Mortgage loans, land \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Mortgage loans, land \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	35,952	29,366
Consumer loans, home equity and second mortgage
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	50,479	47,913
Non-accrual loans	602	618
Recorded Investment			382
Consumer loans, home equity and second mortgage \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Consumer loans, home equity and second mortgage \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	411	0
Consumer loans, home equity and second mortgage \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Consumer loans, home equity and second mortgage \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	1,013	618
Consumer loans, home equity and second mortgage \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	49,466	47,295
Consumer loans, other
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	2,034	3,129
Non-accrual loans	22	0
Recorded Investment			0
Consumer loans, other \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
Consumer loans, other \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	1
Consumer loans, other \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Consumer loans, other \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	22	1
Consumer loans, other \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	2,012	3,128
Commercial business loans
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	126,937	138,743
Non-accrual loans	1,290	2,060
Recorded Investment			$ 286
Commercial business loans \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	374	424
Commercial business loans \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	169
Commercial business loans \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
Commercial business loans \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	1,664	2,653
Commercial business loans \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	125,273	136,090
SBA PPP Loans
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	58	260
Non-accrual loans	0	0
SBA PPP Loans \| 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
SBA PPP Loans \| 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
SBA PPP Loans \| Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0	0
SBA PPP Loans \| Total Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0	0
SBA PPP Loans \| Current
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	$ 58	$ 260

TIMBERLAND BANCORP INC 10-K