Condensed Financial Information - Parent Company Only: Condensed Statements of Operations, Parent Company (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Operating income
Interest on deposits in banks									$ 7,143	$ 3,576	$ 1,117
Interest on investment securities									9,384	3,488	1,195
Income before income taxes and equity in undistributed     income of Bank	$ 8,266	$ 7,972	$ 8,368	$ 9,388	$ 8,835	$ 7,210	$ 6,643	$ 6,874	33,994	29,562	34,428
Benefit for income taxes	1,624	1,666	1,705	1,881	1,785	1,472	1,316	1,389	6,876	5,962	6,845
Net income	$ 6,642	$ 6,306	$ 6,663	$ 7,507	$ 7,050	$ 5,738	$ 5,327	$ 5,485	27,118	23,600	27,583
Parent Company
Operating income
Interest on deposits in banks									0	3	5
Interest on investment securities									24	24	24
Dividends from Bank									11,400	10,255	9,085
Total operating income									11,424	10,282	9,114
Operating expenses									351	303	495
Income before income taxes and equity in undistributed     income of Bank									11,073	9,979	8,619
Benefit for income taxes									(148)	(139)	(238)
Income before undistributed income of Bank									11,221	10,118	8,857
Equity in undistributed income of Bank									15,897	13,482	18,726
Net income									$ 27,118	$ 23,600	$ 27,583