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Summary of Significant Accounting Policies - Other Narrative (Details) |  |  | 12 Months Ended
--- | --- | --- | ---
Oct. 25, 2017 $ / shares | Sep. 27, 2017 extension | Sep. 30, 2017 payment office segment part shares | Sep. 30, 2016 shares | Sep. 30, 2015 shares
Summary of Significant Accounting Policies [Line Items] |  |  |  |  |
Number of offices (in offices) | office |  |  | 237 |  |
Days past grace period to initiate contact to cure deficiency |  |  | 30 days |  |
Minimum days past due to begin foreclosure proceedings |  |  | 90 days |  |
Approximate rate reduction concession, minimum |  |  | 1.00% |  |
Approximate rate reduction concession, maximum |  |  | 2.00% |  |
Minimum days past due to stop accrual of interest |  |  | 90 days |  |
Loans returned to full accrual status |  |  | 90 days |  |
Number of payments required | payment |  |  | 6 |  |
Number of parts in loss percentage factor | part |  |  | 2 |  |
Award vesting period (in years) |  |  | 5 years |  |
Options granted (in shares) | shares |  |  | 0 | 0 | 0
Number of reportable business segments | segment |  |  | 1 |  |
Subsequent Event |  |  |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |  |  |
Dividends declared (in dollars per share) | $ / shares | $ 0.15 |  |  |  |
Anchor Bancorp |  |  |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |  |  |
Number of additional six month extensions | extension |  | 3 |  |  |
Minimum |  |  |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |  |  |
Term for payment and rate reduction |  |  | 6 months |  |
Maximum |  |  |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |  |  |
Term for payment and rate reduction |  |  | 12 months |  |
Options exercisable, weighted average remaining contractual term (in years) |  |  | 10 years |  |
Stock Options and Restricted Stock | Minimum |  |  |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |  |  |
Award vesting period (in years) |  |  | 3 years |  |
Stock Options and Restricted Stock | Maximum |  |  |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |  |  |
Award vesting period (in years) |  |  | 10 years |  |

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