Fair Value Measurements: Schedule of estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Sep. 30, 2022
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in equity securities, at fair value	$ 837	$ 835
Other investments, at cost	3,000	3,000	[1]
Recorded Amount
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	129,953	316,755
CDs held for investment	16,931	22,894
Investment securities	318,895	308,023
Investments in equity securities, at fair value	837	835
FHLB stock	2,802	2,194
Other investments, at cost	3,000	3,000
Loans held for sale		748
Loans receivable, net	1,260,647	1,132,426
Accrued interest receivable	5,451	4,483
Certificates of deposit	251,313	122,584
FHLB borrowings	15,000
Accrued interest payable	881	108
Fair Value
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	129,953	316,755
CDs held for investment	16,767	22,519
Investment securities	304,313	291,198
Investments in equity securities, at fair value	837	835
FHLB stock	2,802	2,194
Other investments, at cost	3,000	3,000
Loans held for sale		758
Loans receivable, net	1,219,328	1,124,579
Accrued interest receivable	5,451	4,483
Certificates of deposit	248,541	120,807
FHLB borrowings	14,665
Accrued interest payable	881	108
Fair Value | Fair Value, Inputs, Level 1
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	129,953	316,755
CDs held for investment	16,767	22,519
Investment securities	161,458	158,578
Investments in equity securities, at fair value	837	835
FHLB stock	2,802	2,194
Other investments, at cost	3,000	3,000
Loans held for sale		758
Loans receivable, net	0	0
Accrued interest receivable	5,451	4,483
Certificates of deposit	0	0
FHLB borrowings	0
Accrued interest payable	881	108
Fair Value | Fair Value, Inputs, Level 2
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
CDs held for investment	0	0
Investment securities	142,855	132,620
Investments in equity securities, at fair value	0	0
FHLB stock	0	0
Other investments, at cost	0	0
Loans held for sale		0
Loans receivable, net	0	0
Accrued interest receivable	0	0
Certificates of deposit	0	0
FHLB borrowings	0
Accrued interest payable	0	0
Fair Value | Fair Value, Inputs, Level 3
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
CDs held for investment	0	0
Investment securities	0	0
Investments in equity securities, at fair value	0	0
FHLB stock	0	0
Other investments, at cost	0	0
Loans held for sale		0
Loans receivable, net	1,219,328	1,124,579
Accrued interest receivable	0	0
Certificates of deposit	248,541	120,807
FHLB borrowings	14,665
Accrued interest payable	$ 0	$ 0

[1] Derived from audited consolidated financial statements.