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Loans Receivable - Loan Modifications (Details) $ in Thousands | 3 Months Ended
--- | ---
Dec. 31, 2017 USD ($) contract | Dec. 31, 2016 USD ($) contract
Financing Receivable, Modifications [Line Items] |  |
Number of contracts | contract | 1 | 8
Recorded investment | $ | $ 44 | $ 2,260
Single-family residential |  |
Financing Receivable, Modifications [Line Items] |  |
Number of contracts | contract | 1 | 6
Recorded investment | $ | $ 44 | $ 1,993
Commercial real estate |  |
Financing Receivable, Modifications [Line Items] |  |
Number of contracts | contract | 0 | 2
Recorded investment | $ | $ 0 | $ 267

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