Fair Value Measurements: Schedule of estimated fair values of financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2022	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	224,896	316,755
CDs held for investment	23,392	22,894
Investment securities	334,426	308,023
Investments in equity securities, at fair value	837	835
FHLB stock	2,194	2,194
Other investments, at cost	3,000	3,000
Loans held for sale		748
Loans receivable, net	1,172,559	1,132,426
Accrued interest receivable	5,508	4,483
Certificates of deposit	152,821	122,584
Accrued interest payable	297	108
Fair Value
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	224,896	316,755
CDs held for investment	23,108	22,519
Investment securities	319,819	291,198
Investments in equity securities, at fair value	837	835
FHLB stock	2,194	2,194
Other investments, at cost	3,000	3,000
Loans held for sale		758
Loans receivable, net	1,134,291	1,124,579
Accrued interest receivable	5,508	4,483
Certificates of deposit	151,441	120,807
Accrued interest payable	297	108
Fair Value | Fair Value, Inputs, Level 1
Fair value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	224,896	316,755
CDs held for investment	23,108	22,519
Investment securities	160,390	158,578
Investments in equity securities, at fair value	837	835
FHLB stock	2,194	2,194
Other investments, at cost	3,000	3,000
Loans held for sale		758
Loans receivable, net	0	0
Accrued interest receivable	5,508	4,483
Certificates of deposit	0	0
Accrued interest payable	297	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	159,429	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
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	1,134,291	1,124,579
Accrued interest receivable	0	0
Certificates of deposit	151,441	120,807
Accrued interest payable	$ 0	$ 0

[1] Derived from audited consolidated financial statements.