Fair Value Accounting - Assets Measured on a Nonrecurring Basis (Details) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Assets Measured on a Nonrecurring Basis
Foreclosed and repossessed assets, net	$ 6,017	$ 776
Impaired loans with allocated allowances	1,490	2,412
Total	9,458	3,188
Quoted Prices in Active Markets for Identical Instruments (Level 1)
Assets Measured on a Nonrecurring Basis
Foreclosed and repossessed assets, net	0	0
Impaired loans with allocated allowances	0	0
Total	0	0
Significant Other Observable Inputs (Level 2)
Assets Measured on a Nonrecurring Basis
Foreclosed and repossessed assets, net	0	0
Impaired loans with allocated allowances	0	0
Total	0	0
Significant Unobservable Inputs (Level 3)
Assets Measured on a Nonrecurring Basis
Foreclosed and repossessed assets, net	6,017	776
Impaired loans with allocated allowances	1,490	2,412
Total	9,458	$ 3,188
Mortgage servicing rights
Assets Measured on a Nonrecurring Basis
Mortgage servicing rights	1,951
Mortgage servicing rights | Significant Unobservable Inputs (Level 3)
Assets Measured on a Nonrecurring Basis
Mortgage servicing rights	$ 1,951