Investment Securities: Schedule of Contractual maturities of debt securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Held-to-maturity Securities, Amortized Cost:
Due within one year	$ 3,013
Due after one year to five years	189
Due after five years to ten years	5,852
Due after ten years	30,026
Total	39,080	$ 31,102	[1]
Held-to-maturity Securities, Estimated Fair Value:
Due within one year	3,011
Due after one year to five years	193
Due after five years to ten years	6,153
Due after ten years	30,883
Total	40,240	$ 32,580
Available-for-sale Securities, Amortized Cost:
Due within one year	0
Due after one year to five years	133
Due after five years to ten years	1,432
Due after ten years	36,455
Total	38,020
Available-for-sale Securities, Estimated Fair Value:
Due within one year	0
Due after one year to five years	133
Due after five years to ten years	1,427
Due after ten years	36,313
Total	$ 37,873

[1] Derived from audited consolidated financial statements.