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DERIVATIVE INSTRUMENTS - VOLUME (Details) certificate in Thousands | Dec. 31, 2017 USD ($) Bcf certificate | Sep. 30, 2017 Bcf | Jun. 01, 2015 USD ($)
--- | --- | --- | ---
Derivative [Line Items] |  |  |
Derivative, notional amount | $ |  |  | $ 125,000,000
Foreign currency contracts |  |  |
Derivative [Line Items] |  |  |
Derivative, notional amount | $ | $ 9,700,000 |  |
Natural Gas Distribution | Long | Futures |  |  |
Derivative [Line Items] |  |  |
Volume | (20.4) | (18.2) |
Natural Gas Distribution | Long | Physical |  |  |
Derivative [Line Items] |  |  |
Volume | (26.8) | (32.1) |
Energy Services | Physical commodity contracts |  |  |
Derivative [Line Items] |  |  |
Number of SRECs | certificate | 403 |  |
Energy Services | Short | Futures |  |  |
Derivative [Line Items] |  |  |
Volume | (33.4) | (16.4) |
Energy Services | Short | Physical |  |  |
Derivative [Line Items] |  |  |
Volume | (4.6) | (13.1) |

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