Investment Securities: Schedule of Contractual maturities of debt securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Held-to-maturity Securities, Amortized Cost:
Due within one year	$ 83,614
Due after one year to five years	105,308
Due after five years to ten years	10,510
Due after ten years	70,786
Total	270,218	$ 266,608
Held-to-maturity Securities, Estimated Fair Value:
Due within one year	82,258
Due after one year to five years	96,743
Due after five years to ten years	9,428
Due after ten years	65,337
Total	253,766	249,783
Available-for-sale Securities, Amortized Cost:
Due within one year	388
Due after one year to five years	2,608
Due after five years to ten years	6,689
Due after ten years	33,447
Total	43,132	$ 42,309
Available-for-sale Securities, Estimated Fair Value:
Due within one year	385
Due after one year to five years	2,590
Due after five years to ten years	6,642
Due after ten years	32,154
Total	$ 41,771