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, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	$ 247	$ 41
Allowance for Loan Losses, Collectively Evaluated for Impairment	13,222	13,373
Allowance for Loan Losses, Total	13,469	13,414	$ 9,690	$ 9,530
Recorded Investment in Loans, Individually Evaluated for Impairment	5,224	5,773
Recorded Investment in Loans, Collectively Evaluated for Impairment	981,842	1,027,952
Loans receivable	987,066	1,033,725
Mortgage loans, one-to-four family
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	0	3
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,154	1,160
Allowance for Loan Losses, Total	1,154	1,163	1,167	1,086
Recorded Investment in Loans, Individually Evaluated for Impairment	407	1,143
Recorded Investment in Loans, Collectively Evaluated for Impairment	119,528	117,437
Loans receivable	119,935	118,580
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	765	718
Allowance for Loan Losses, Total	765	718	481	433
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	87,563	85,053
Loans receivable	87,563	85,053
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	6,813	7,144
Allowance for Loan Losses, Total	6,813	7,144	4,154	4,248
Recorded Investment in Loans, Individually Evaluated for Impairment	3,143	3,242
Recorded Investment in Loans, Collectively Evaluated for Impairment	467,507	450,332
Loans receivable	470,650	453,574
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	644	832
Allowance for Loan Losses, Total	644	832	755	671
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	61,003	75,332
Loans receivable	61,003	75,332
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	188	158
Allowance for Loan Losses, Total	188	158	212	178
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	9,657	7,108
Loans receivable	9,657	7,108
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	784	420
Allowance for Loan Losses, Total	784	420	338	563
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	38,931	20,927
Loans receivable	38,931	20,927
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	436	238
Allowance for Loan Losses, Total	436	238	375	135
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	22,888	10,832
Loans receivable	22,888	10,832
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	124	133
Allowance for Loan Losses, Total	124	133	67	49
Recorded Investment in Loans, Individually Evaluated for Impairment	0	0
Recorded Investment in Loans, Collectively Evaluated for Impairment	5,502	4,739
Loans receivable	5,502	4,739
Mortgage loans, land
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	76	0
Allowance for Loan Losses, Collectively Evaluated for Impairment	394	572
Allowance for Loan Losses, Total	470	572	697	844
Recorded Investment in Loans, Individually Evaluated for Impairment	683	394
Recorded Investment in Loans, Collectively Evaluated for Impairment	19,253	25,177
Loans receivable	19,936	25,571
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	528	593
Allowance for Loan Losses, Total	528	593	623	649
Recorded Investment in Loans, Individually Evaluated for Impairment	516	555
Recorded Investment in Loans, Collectively Evaluated for Impairment	32,472	31,522
Loans receivable	32,988	32,077
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	50	71
Allowance for Loan Losses, Total	50	71	99	117
Recorded Investment in Loans, Individually Evaluated for Impairment	17	9
Recorded Investment in Loans, Collectively Evaluated for Impairment	2,495	3,563
Loans receivable	2,512	3,572
Commercial business loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Loan Losses, Individually Evaluated for Impairment	171	38
Allowance for Loan Losses, Collectively Evaluated for Impairment	1,342	1,334
Allowance for Loan Losses, Total	1,513	1,372	$ 722	$ 557
Recorded Investment in Loans, Individually Evaluated for Impairment	458	430
Recorded Investment in Loans, Collectively Evaluated for Impairment	74,121	69,110
Loans receivable	74,579	69,540
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	40,922	126,820
Loans receivable	$ 40,922	$ 126,820