Investment Securities: Schedule of Contractual maturities of debt securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Sep. 30, 2022
Held-to-maturity Securities, Amortized Cost:
Due within one year	$ 86,147
Due after one year to five years	96,893
Due after five years to ten years	19,448
Due after ten years	72,565
Total	275,053	$ 266,608	[1]
Held-to-maturity Securities, Estimated Fair Value:
Due within one year	84,077
Due after one year to five years	90,103
Due after five years to ten years	17,541
Due after ten years	68,750
Total	260,471	$ 249,783
Available-for-sale Securities, Amortized Cost:
Due within one year	0
Due after one year to five years	3,049
Due after five years to ten years	7,103
Due after ten years	34,620
Total	44,772
Available-for-sale Securities, Estimated Fair Value:
Due within one year	0
Due after one year to five years	3,024
Due after five years to ten years	7,045
Due after ten years	33,773
Total	$ 43,842

[1] Derived from audited consolidated financial statements.