Investment Securities: Schedule of Contractual maturities of debt securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022
Held-to-maturity Securities, Amortized Cost:
Due within one year	$ 54,872
Due after one year to five years	123,311
Due after five years to ten years	25,082
Due after ten years	74,646
Total	277,911	$ 266,608	[1]
Held-to-maturity Securities, Estimated Fair Value:
Due within one year	53,419
Due after one year to five years	117,192
Due after five years to ten years	22,814
Due after ten years	71,667
Total	265,092	$ 249,783
Available-for-sale Securities, Amortized Cost:
Due within one year	0
Due after one year to five years	3,200
Due after five years to ten years	7,653
Due after ten years	44,601
Total	55,454
Available-for-sale Securities, Estimated Fair Value:
Due within one year	0
Due after one year to five years	3,180
Due after five years to ten years	7,624
Due after ten years	44,034
Total	$ 54,838

[1] Derived from audited consolidated financial statements.