Loans Receivable and Allowance for Loan Losses: COVID Modifications (Details) $ in Thousands	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 USD ($) loan
Financing Receivable, Impaired [Line Items]
Number of mortgage loans modified | loan	1	5
Loans Receivable, Including Loans Held-For-Sale, Excluding Loans in Process and Deferred Fees, Gross, Mortgage Loans, Modified For COVID	$ 323
Loans Receivable, Ratio of Loan Category to Total Loans, Modified For COVID	100.00%	100.00%
Loans Receivable, Including Loans Held-For-Sale, Excluding Loans In Process And Deferred Fees, Gross, Commercial, Modified For COVID	$ 323	$ 5,870
Mortgage loans, one-to-four family
Financing Receivable, Impaired [Line Items]
Number of mortgage loans modified | loan	1	1
Loans Receivable, Including Loans Held-For-Sale, Excluding Loans in Process and Deferred Fees, Gross, Mortgage Loans, Modified For COVID	$ 323	$ 467
Loans Receivable, Ratio of Loan Category to Total Loans, Modified For COVID	100.00%	8.00%
Mortgage loans, commercial
Financing Receivable, Impaired [Line Items]
Number of mortgage loans modified | loan		2
Loans Receivable, Including Loans Held-For-Sale, Excluding Loans in Process and Deferred Fees, Gross, Mortgage Loans, Modified For COVID		$ 3,951
Loans Receivable, Ratio of Loan Category to Total Loans, Modified For COVID		67.20%
Mortgage Loans Construction [Member]
Financing Receivable, Impaired [Line Items]
Number of mortgage loans modified | loan		1
Loans Receivable, Including Loans Held-For-Sale, Excluding Loans in Process and Deferred Fees, Gross, Mortgage Loans, Modified For COVID		$ 1,402
Loans Receivable, Ratio of Loan Category to Total Loans, Modified For COVID		23.90%
Total mortgage loans
Financing Receivable, Impaired [Line Items]
Number of mortgage loans modified | loan		4
Loans Receivable, Including Loans Held-For-Sale, Excluding Loans in Process and Deferred Fees, Gross, Mortgage Loans, Modified For COVID		$ 5,820
Loans Receivable, Ratio of Loan Category to Total Loans, Modified For COVID		99.10%
Consumer loans, home equity and second mortgage
Financing Receivable, Impaired [Line Items]
Number of mortgage loans modified | loan		1
Loans Receivable, Ratio of Loan Category to Total Loans, Modified For COVID		0.90%
Loans Receivable, Including Loans Held-For-Sale, Excluding Loans In Process And Deferred Fees, Gross, Consumer, Modified For COVID		$ 50
Total consumer loans
Financing Receivable, Impaired [Line Items]
Number of mortgage loans modified | loan		1
Loans Receivable, Ratio of Loan Category to Total Loans, Modified For COVID		0.90%
Loans Receivable, Including Loans Held-For-Sale, Excluding Loans In Process And Deferred Fees, Gross, Consumer, Modified For COVID		$ 50