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Derivatives and Hedging Activities (Details) - USD ($) | 3 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2017
Derivative [Line Items] |  |  |
Gain (loss) on derivative instruments | $ 0 | $ 0 |
Derivative asset, fair value | 12,584,000 |  | $ 1,139,000
Derivative liability, fair value | 7,623,000 |  | 3,006,000
Interest rate swap agreements |  |  |
Derivative [Line Items] |  |  |
Customer derivatives program | 956,247,000 |  | 1,035,573,000
Notional amount | 700,000,000 | $ 700,000,000 |
Commercial loan interest rate swap |  |  |
Derivative [Line Items] |  |  |
Notional amount | 97,927,000 |  | 52,936,000
Interest rate contracts | Other assets |  |  |
Derivative [Line Items] |  |  |
Derivative asset, fair value | 7,587,000 |  | 1,139,000
Interest rate contracts | Other liabilities |  |  |
Derivative [Line Items] |  |  |
Derivative liability, fair value | 7,587,000 |  | 1,139,000
Commercial loan hedges | Other assets |  |  |
Derivative [Line Items] |  |  |
Derivative asset, fair value | 0 |  | 0
Commercial loan hedges | Other liabilities |  |  |
Derivative [Line Items] |  |  |
Derivative liability, fair value | 36,000 |  | 174,000
Borrowings hedges | Other assets |  |  |
Derivative [Line Items] |  |  |
Derivative asset, fair value | 4,997,000 |  | 0
Borrowings hedges | Other liabilities |  |  |
Derivative [Line Items] |  |  |
Derivative liability, fair value | $ 0 |  | $ 1,693,000

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