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Loans - Narrative, Troubled Debt Restructurings (Details) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2020 USD ($) contract | Mar. 31, 2019 USD ($) contract | Jun. 30, 2018 contract | Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Number of relationships (contract) | contract | 0 | 2 |  |
Pre-Modification Outstanding Recorded Investment |  | $ 2,836 |  |
Post-Modification Outstanding Recorded Investment |  | $ 2,836 |  |
Troubled debt restructurings | $ 17,100 |  |  | $ 18,500
Number of TDR loans restructured that subsequently defaulted (contract) | contract | 1 | 0 | 0 |
Loans restructured that subsequently defaulted | $ 27 |  |  |
One-to-Four Family |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Number of relationships (contract) | contract |  | 1 |  |
Pre-Modification Outstanding Recorded Investment |  | $ 2 |  |
Post-Modification Outstanding Recorded Investment |  | $ 2 |  |
Commercial Mortgage Backed Securities |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |
Number of relationships (contract) | contract |  | 1 |  |
Pre-Modification Outstanding Recorded Investment |  | $ 2,834 |  |
Post-Modification Outstanding Recorded Investment |  | $ 2,834 |  |

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