Fair Value Measurements - Non-recurring (Details) - Nonrecurring - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	$ 398
Commercial business loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	177
Total impaired loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	177	$ 1,315
OREO and other repossessed items
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	221
Fair Value, Inputs, Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	0
Fair Value, Inputs, Level 1 | Commercial business loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	0
Fair Value, Inputs, Level 1 | Total impaired loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	0	0
Fair Value, Inputs, Level 1 | OREO and other repossessed items
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	0
Fair Value, Inputs, Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	0
Fair Value, Inputs, Level 2 | Commercial business loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	0
Fair Value, Inputs, Level 2 | Total impaired loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	0	0
Fair Value, Inputs, Level 2 | OREO and other repossessed items
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	0
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	398
Fair Value, Inputs, Level 3 | Commercial business loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	177
Fair Value, Inputs, Level 3 | Total impaired loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	177	$ 1,315
Fair Value, Inputs, Level 3 | OREO and other repossessed items
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets, estimated fair value, nonrecurring	$ 221