Loans Receivable and Allowance for Loan Losses: Schedule of Allowance for Loan Losses (Details) - USD ($)	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	$ 15,817,000	$ 13,703,000	$ 13,469,000
Provision for credit losses - loans	1,254,000	2,132,000	270,000
Charge-offs	(101,000)	(19,000)	(59,000)
Recoveries	47,000	1,000	23,000
Allowance for loan losses, Ending Allowance	17,478,000	15,817,000	13,703,000
Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	461,000
Allowance for loan losses, Ending Allowance		461,000
Mortgage loans, one-to-four family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	2,417,000	1,658,000	1,154,000
Provision for credit losses - loans	580,000	759,000	504,000
Charge-offs	0	0	0
Recoveries	43,000	0	0
Allowance for loan losses, Ending Allowance	2,632,000	2,417,000	1,658,000
Mortgage loans, one-to-four family | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	(408,000)
Allowance for loan losses, Ending Allowance		(408,000)
Mortgage loans, multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	1,156,000	855,000	765,000
Provision for credit losses - loans	272,000	301,000	90,000
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	1,308,000	1,156,000	855,000
Mortgage loans, multi-family | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	(120,000)
Allowance for loan losses, Ending Allowance		(120,000)
Mortgage loans, commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	7,209,000	6,682,000	6,813,000
Provision for credit losses - loans	219,000	527,000	(131,000)
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	6,934,000	7,209,000	6,682,000
Mortgage loans, commercial | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	(494,000)
Allowance for loan losses, Ending Allowance		(494,000)
Mortgage loans, construction - custom and owner/builder
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	750,000	675,000	644,000
Provision for credit losses - loans	36,000	75,000	31,000
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	1,328,000	750,000	675,000
Mortgage loans, construction - custom and owner/builder | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	542,000
Allowance for loan losses, Ending Allowance		542,000
Mortgage loans, construction - speculative one-to-four family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	148,000	130,000	188,000
Provision for credit losses - loans	(4,000)	18,000	(58,000)
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	128,000	148,000	130,000
Mortgage loans, construction - speculative one-to-four family | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	(16,000)
Allowance for loan losses, Ending Allowance		(16,000)
Mortgage loans, construction - commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	316,000	343,000	784,000
Provision for credit losses - loans	45,000	(27,000)	(441,000)
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	537,000	316,000	343,000
Mortgage loans, construction - commercial | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	176,000
Allowance for loan losses, Ending Allowance		176,000
Mortgage loans, construction - multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	602,000	447,000	436,000
Provision for credit losses - loans	(350,000)	155,000	11,000
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	456,000	602,000	447,000
Mortgage loans, construction - multi-family | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	204,000
Allowance for loan losses, Ending Allowance		204,000
Mortgage loans - construction - land development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	274,000	233,000	124,000
Provision for credit losses - loans	36,000	41,000	109,000
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	335,000	274,000	233,000
Mortgage loans - construction - land development | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	25,000
Allowance for loan losses, Ending Allowance		25,000
Mortgage loans, land
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	406,000	397,000	470,000
Provision for credit losses - loans	69,000	9,000	(73,000)
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	793,000	406,000	397,000
Mortgage loans, land | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	318,000
Allowance for loan losses, Ending Allowance		318,000
Consumer loans, home equity and second mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	519,000	440,000	528,000
Provision for credit losses - loans	72,000	79,000	(88,000)
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	348,000	519,000	440,000
Consumer loans, home equity and second mortgage | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	(243,000)
Allowance for loan losses, Ending Allowance		(243,000)
Consumer loans, other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	53,000	42,000	50,000
Provision for credit losses - loans	2,000	14,000	1,000
Charge-offs	(9,000)	(4,000)	(10,000)
Recoveries	0	1,000	1,000
Allowance for loan losses, Ending Allowance	39,000	53,000	42,000
Consumer loans, other | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	(7,000)
Allowance for loan losses, Ending Allowance		(7,000)
Commercial business loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	1,967,000	1,801,000	1,513,000
Provision for credit losses - loans	277,000	181,000	315,000
Charge-offs	(92,000)	(15,000)	(49,000)
Recoveries	4,000	0	22,000
Allowance for loan losses, Ending Allowance	2,640,000	1,967,000	$ 1,801,000
Commercial business loans | Impact of Adopting CECL (ASU 2016-13)
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	$ 484,000
Allowance for loan losses, Ending Allowance		$ 484,000