Fair Value Measurements: Level 3 Fair Value Measurements, Nonrecurring (Details) - Nonrecurring - Fair Value, Inputs, Level 3 - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, estimated fair value, nonrecurring	$ 566	$ 1,741
Total impaired loans
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, estimated fair value, nonrecurring	409	691
OREO and other repossessed assets
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, estimated fair value, nonrecurring	157	1,050
Market approach | Total impaired loans
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, estimated fair value, nonrecurring	409	691
Market approach | OREO and other repossessed assets
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Assets, estimated fair value, nonrecurring	$ 157	$ 1,050