Loans Receivable and Allowance for Loan Losses: Impaired Financing Receivables (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	$ 3,764	$ 4,282
Impaired Financing Receivable, with Related Allowance, Recorded Investment	245	250
Impaired Financing Receivable, Recorded Investment	4,009	4,532
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	3,857	4,375
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	245	250
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	4,102	4,625
Related Allowance	123	127
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	4,102	4,567
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	247	413
Impaired Financing Receivable, Average Recorded Investment	4,349	4,980
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	213	189
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	0	0
Impaired Financing Receivable, Interest Income Recognized	213	189
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	172	159
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized	0	0
Impaired Financing Receivable, Cash Basis Interest Income Recognized	172	159
Mortgage loans, one-to-four family
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	368	388
Impaired Financing Receivable, Recorded Investment	368	388
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	412	432
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	412	432
Related Allowance	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	378	470
Impaired Financing Receivable, Average Recorded Investment	378	470
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	29	31
Impaired Financing Receivable, Interest Income Recognized	29	31
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	29	31
Impaired Financing Receivable, Cash Basis Interest Income Recognized	29	31
Mortgage loans, commercial
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	2,973	2,988
Impaired Financing Receivable, Recorded Investment	2,973	2,988
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	2,973	2,988
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	2,973	2,988
Related Allowance	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	2,987	3,041
Impaired Financing Receivable, Average Recorded Investment	2,987	3,041
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	167	152
Impaired Financing Receivable, Interest Income Recognized	167	152
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	129	123
Impaired Financing Receivable, Cash Basis Interest Income Recognized	129	123
Mortgage loans, land
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	450
Impaired Financing Receivable, Recorded Investment	0	450
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	450
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	450
Related Allowance	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	297	492
Impaired Financing Receivable, Average Recorded Investment	297	492
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	5	0
Impaired Financing Receivable, Interest Income Recognized	5	0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	4	0
Impaired Financing Receivable, Cash Basis Interest Income Recognized	4	0
Consumer loans, home equity and second mortgage
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	382	394
Impaired Financing Receivable, with Related Allowance, Recorded Investment		0
Impaired Financing Receivable, Recorded Investment	382	394
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	382	394
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)		0
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	382	394
Related Allowance	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	390	436
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		145
Impaired Financing Receivable, Average Recorded Investment	390	581
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	12	6
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized		0
Impaired Financing Receivable, Interest Income Recognized	12	6
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	10	5
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized		0
Impaired Financing Receivable, Cash Basis Interest Income Recognized	10	5
Consumer loans, other
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment		3
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)		3
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		7
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized		0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized		0
Consumer loans, other
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0
Impaired Financing Receivable, Recorded Investment	0	3
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	3
Related Allowance	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1
Impaired Financing Receivable, Average Recorded Investment	1	7
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	0
Impaired Financing Receivable, Interest Income Recognized	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	0
Impaired Financing Receivable, Cash Basis Interest Income Recognized	0	0
Commercial business loans
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	41	59
Impaired Financing Receivable, with Related Allowance, Recorded Investment	245	250
Impaired Financing Receivable, Recorded Investment	286	309
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	90	108
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	245	250
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	335	358
Related Allowance	123	127
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	49	121
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	247	268
Impaired Financing Receivable, Average Recorded Investment	296	389
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	0	0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	0	0
Impaired Financing Receivable, Interest Income Recognized	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	0	0
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized	0	0
Impaired Financing Receivable, Cash Basis Interest Income Recognized	$ 0	$ 0