Premises and Equipment: Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 41,590	$ 40,601
Less accumulated depreciation	19,948	18,703
Premises and equipment, net	21,642	21,898
Land
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	5,404	5,404
Buildings and improvements
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	25,178	24,764
Furniture and equipment
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	10,715	10,152
Property held for future expansion
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	116	129
Construction and purchases in progress
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 177	$ 152