Loans Receivable and Allowance for Loan Losses: Schedule of Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	$ 9,690	$ 9,530	$ 9,553
Provision for (Recapture of) Loan Losses	3,700	0	0
Charge-offs	(27)	(161)	(56)
Recoveries	51	321	33
Allowance for loan losses, Ending Allowance	13,414	9,690	9,530
Mortgage loans, one-to-four family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	1,167	1,086	1,082
Provision for (Recapture of) Loan Losses	(6)	(23)	4
Charge-offs	0	0	0
Recoveries	2	104	0
Allowance for loan losses, Ending Allowance	1,163	1,167	1,086
Mortgage loans, multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	481	433	447
Provision for (Recapture of) Loan Losses	237	48	(14)
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	718	481	433
Mortgage loans, commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	4,154	4,248	4,184
Provision for (Recapture of) Loan Losses	2,984	(260)	92
Charge-offs	0	0	(28)
Recoveries	6	166	0
Allowance for loan losses, Ending Allowance	7,144	4,154	4,248
Mortgage loans, construction - custom and owner/builder
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	755	671	699
Provision for (Recapture of) Loan Losses	72	82	(28)
Charge-offs	0	0	0
Recoveries	5	2	0
Allowance for loan losses, Ending Allowance	832	755	671
Mortgage loans, construction - speculative one-to-four family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	212	178	128
Provision for (Recapture of) Loan Losses	(54)	34	37
Charge-offs	0	0	0
Recoveries	0	0	13
Allowance for loan losses, Ending Allowance	158	212	178
Mortgage loans, construction - commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	338	563	303
Provision for (Recapture of) Loan Losses	82	(225)	260
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	420	338	563
Mortgage loans, construction - multi-family
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	375	135	173
Provision for (Recapture of) Loan Losses	(137)	240	(38)
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	238	375	135
Mortgage loans - construction - land development
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	67	49	0
Provision for (Recapture of) Loan Losses	66	18	49
Charge-offs	0	0	0
Recoveries	0	0	0
Allowance for loan losses, Ending Allowance	133	67	49
Mortgage loans, land
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	697	844	918
Provision for (Recapture of) Loan Losses	(145)	(116)	(71)
Charge-offs	0	(49)	(22)
Recoveries	20	18	19
Allowance for loan losses, Ending Allowance	572	697	844
Consumer loans, home equity and second mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	623	649	983
Provision for (Recapture of) Loan Losses	(45)	(21)	(334)
Charge-offs	0	(5)	0
Recoveries	15	0	0
Allowance for loan losses, Ending Allowance	593	623	649
Consumer loans, other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	99	117	121
Provision for (Recapture of) Loan Losses	(19)	(19)	1
Charge-offs	(12)	(5)	(6)
Recoveries	3	6	1
Allowance for loan losses, Ending Allowance	71	99	117
Commercial business loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses, Beginning Allowance	722	557	515
Provision for (Recapture of) Loan Losses	665	242	42
Charge-offs	(15)	(102)	0
Recoveries	0	25	0
Allowance for loan losses, Ending Allowance	$ 1,372	$ 722	$ 557

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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