Federal Income Taxes: Schedule of Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Federal									$ 6,570	$ 5,962	$ 5,198
Deferred									275	76	703
Provision for income taxes	$ 1,525	$ 1,786	$ 1,651	$ 1,883	$ 1,635	$ 1,463	$ 1,225	$ 1,715	$ 6,845	$ 6,038	$ 5,901