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Fair Value Measurements - Recurring and Nonrecurring (Details) - USD ($) $ in Thousands | 3 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | $ 1,245,855 |  | $ 1,266,209
Total financial assets | 2,999,197 |  | 2,902,122
Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 1,245,855 |  | 1,266,209
Interest rate contracts |  |  | 1,139
Total financial assets | 1,258,439 |  | 1,267,348
Total financial liabilities | 7,623 |  | 3,006
Recurring | Interest rate contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 7,587 |  |
Interest rate contracts | 7,587 |  | 1,139
Recurring | Commercial loan hedges |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 36 |  | 174
Recurring | Borrowings hedges |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 4,997 |  |
Interest rate contracts |  |  | 1,693
Recurring | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 503 |  | 522
Recurring | U.S. government and agency securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 194,869 |  | 211,077
Recurring | Municipal bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 26,212 |  | 26,624
Recurring | Corporate debt securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 184,416 |  | 185,298
Recurring | Agency pass-through certificates |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 831,489 |  | 834,297
Recurring | Commercial MBS |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 8,366 |  | 8,391
Recurring | Level 1 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 503 |  | 522
Interest rate contracts |  |  | 0
Total financial assets | 503 |  | 522
Total financial liabilities | 0 |  | 0
Recurring | Level 1 | Interest rate contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 0 |  |
Interest rate contracts | 0 |  | 0
Recurring | Level 1 | Commercial loan hedges |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 0 |  | 0
Recurring | Level 1 | Borrowings hedges |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 0 |  |
Interest rate contracts |  |  | 0
Recurring | Level 1 | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 503 |  | 522
Recurring | Level 1 | U.S. government and agency securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 1 | Municipal bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 1 | Corporate debt securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 1 | Agency pass-through certificates |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 1 | Commercial MBS |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 2 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 1,245,352 |  | 1,265,687
Interest rate contracts |  |  | 1,139
Total financial assets | 1,257,936 |  | 1,266,826
Total financial liabilities | 7,623 |  | 3,006
Recurring | Level 2 | Interest rate contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 7,587 |  |
Interest rate contracts | 7,587 |  | 1,139
Recurring | Level 2 | Commercial loan hedges |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 36 |  | 174
Recurring | Level 2 | Borrowings hedges |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 4,997 |  |
Interest rate contracts |  |  | 1,693
Recurring | Level 2 | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 2 | U.S. government and agency securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 194,869 |  | 211,077
Recurring | Level 2 | Municipal bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 26,212 |  | 26,624
Recurring | Level 2 | Corporate debt securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 184,416 |  | 185,298
Recurring | Level 2 | Agency pass-through certificates |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 831,489 |  | 834,297
Recurring | Level 2 | Commercial MBS |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 8,366 |  | 8,391
Recurring | Level 3 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Interest rate contracts |  |  | 0
Total financial assets | 0 |  | 0
Total financial liabilities | 0 |  | 0
Recurring | Level 3 | Interest rate contracts |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 0 |  |
Interest rate contracts | 0 |  | 0
Recurring | Level 3 | Commercial loan hedges |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 0 |  | 0
Recurring | Level 3 | Borrowings hedges |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Interest rate contracts | 0 |  |
Interest rate contracts |  |  | 0
Recurring | Level 3 | Equity securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 3 | U.S. government and agency securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 3 | Municipal bonds |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 3 | Corporate debt securities |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 3 | Agency pass-through certificates |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | 0
Recurring | Level 3 | Commercial MBS |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Available-for-sale securities, at fair value | 0 |  | $ 0
Nonrecurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 2,743 | $ 5,652 |
Nonrecurring | Changes Measurement |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Loss related to impaired loans and real estate held for sale, measured on nonrecurring basis | (687) | (663) |
Nonrecurring | Impaired loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 688 | 3,353 |
Nonrecurring | Impaired loans | Changes Measurement |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Loss related to impaired loans and real estate held for sale, measured on nonrecurring basis | (507) | (422) |
Nonrecurring | Real Estate Owned |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 2,055 | 2,299 |
Nonrecurring | Real Estate Owned | Changes Measurement |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Loss related to impaired loans and real estate held for sale, measured on nonrecurring basis | (180) | (241) |
Nonrecurring | Level 1 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 0 | 0 |
Nonrecurring | Level 1 | Impaired loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 0 | 0 |
Nonrecurring | Level 1 | Real Estate Owned |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 0 | 0 |
Nonrecurring | Level 2 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 0 | 0 |
Nonrecurring | Level 2 | Impaired loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 0 | 0 |
Nonrecurring | Level 2 | Real Estate Owned |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 0 | 0 |
Nonrecurring | Level 3 |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 2,743 | 5,652 |
Nonrecurring | Level 3 | Impaired loans |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | 688 | 3,353 |
Nonrecurring | Level 3 | Real Estate Owned |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Assets, nonrecurring | $ 2,055 | $ 2,299 |

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