Loans Receivable and Allowance for Loan Losses: Schedule of loans evaluated individually for impairment and collectively evaluated for impairment in the allowance for loan losses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	$ 123	$ 127
Allowance for Loan Losses, Collectively Evaluated for Impairment	15,694	13,576
Allowance for Loan Losses, Total	15,817	13,703	$ 13,469	$ 13,414
Recorded Investment in Loans, Individually Evaluated for Impairment	4,009	4,532
Recorded Investment in Loans, Collectively Evaluated for Impairment	1,319,355	1,145,918
Loans receivable	1,323,364	1,150,450
Mortgage loans, one-to-four family
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	2,417	1,658
Allowance for Loan Losses, Total	2,417	1,658	1,154	1,163
Recorded Investment in Loans, Individually Evaluated for Impairment	368	388
Recorded Investment in Loans, Collectively Evaluated for Impairment	252,859	175,728
Loans receivable	253,227	176,116
Mortgage loans, multi-family
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,156	855
Allowance for Loan Losses, Total	1,156	855	765	718
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	127,176	95,025
Loans receivable	127,176	95,025
Mortgage loans, commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	7,209	6,682
Allowance for Loan Losses, Total	7,209	6,682	6,813	7,144
Recorded Investment in Loans, Individually Evaluated for Impairment	2,973	2,988
Recorded Investment in Loans, Collectively Evaluated for Impairment	565,292	533,662
Loans receivable	568,265	536,650
Mortgage loans, construction - custom and owner/builder
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	750	675
Allowance for Loan Losses, Total	750	675	644	832
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	73,239	67,091
Loans receivable	73,239	67,091
Mortgage loans, construction - speculative one-to-four family
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	148	130
Allowance for Loan Losses, Total	148	130	188	158
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	9,361	8,364
Loans receivable	9,361	8,364
Mortgage loans, construction - commercial
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	316	343
Allowance for Loan Losses, Total	316	343	784	420
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	26,030	29,059
Loans receivable	26,030	29,059
Mortgage loans, construction - multi-family
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	602	447
Allowance for Loan Losses, Total	602	447	436	238
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	45,890	34,354
Loans receivable	45,890	34,354
Mortgage loans - construction - land development
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	274	233
Allowance for Loan Losses, Total	274	233	124	133
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	16,129	13,582
Loans receivable	16,129	13,582
Mortgage loans, land
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	406	397
Allowance for Loan Losses, Total	406	397	470	572
Recorded Investment in Loans, Individually Evaluated for Impairment	0	450
Recorded Investment in Loans, Collectively Evaluated for Impairment	26,726	26,404
Loans receivable	26,726	26,854
Consumer loans, home equity and second mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	519	440
Allowance for Loan Losses, Total	519	440	528	593
Recorded Investment in Loans, Individually Evaluated for Impairment	382	394
Recorded Investment in Loans, Collectively Evaluated for Impairment	37,899	34,793
Loans receivable	38,281	35,187
Consumer loans, other
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	53	42
Allowance for Loan Losses, Total	53	42	50	71
Recorded Investment in Loans, Individually Evaluated for Impairment	0	3
Recorded Investment in Loans, Collectively Evaluated for Impairment	2,772	2,125
Loans receivable	2,772	2,128
Commercial business loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	123	127
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,844	1,674
Allowance for Loan Losses, Total	1,967	1,801	$ 1,513	$ 1,372
Recorded Investment in Loans, Individually Evaluated for Impairment	286	309
Recorded Investment in Loans, Collectively Evaluated for Impairment	135,516	124,730
Loans receivable	135,802	125,039
SBA PPP Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	0	0
Allowance for Loan Losses, Total	0	0
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	466	1,001
Loans receivable	$ 466	$ 1,001