Investment Securities: Schedule of Contractual maturities of debt securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Sep. 30, 2022
Held-to-maturity Securities, Amortized Cost:
Due within one year	$ 6,010
Due after one year to five years	161,301
Due after five years to ten years	36,374
Due after ten years	74,900
Total	278,585	$ 266,608	[1]
Held-to-maturity Securities, Estimated Fair Value:
Due within one year	5,877
Due after one year to five years	153,803
Due after five years to ten years	32,672
Due after ten years	71,626
Total	263,978	$ 249,783
Available-for-sale Securities, Amortized Cost:
Due within one year	0
Due after one year to five years	2,913
Due after five years to ten years	8,439
Due after ten years	45,408
Total	56,760
Available-for-sale Securities, Estimated Fair Value:
Due within one year	0
Due after one year to five years	2,895
Due after five years to ten years	8,313
Due after ten years	44,633
Total	$ 55,841

[1] Derived from audited consolidated financial statements.