|
Derivatives (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
|
3 Months Ended |
12 Months Ended |
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|
Mar. 31, 2015
|
Mar. 31, 2014
|
Dec. 31, 2016
|
Dec. 31, 2015
|
Dec. 31, 2014
|
| Derivative [Line Items] |
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|
|
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| Current liability for the obligation to return cash collateral |
$ 0.7 |
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|
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| Current asset for the right to reclaim cash collateral |
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|
2.4 |
| Gain on derivative contracts designated as hedge instruments in cash flow hedges to be reclassified from OCI into earnings during the next twelve months |
6.3 |
|
|
|
|
| Net unrealized and realized gains (losses) related to trading portfolio |
(1.0) |
(0.4) |
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|
| Scenario, Forecast [Member] |
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| Derivative [Line Items] |
|
|
|
|
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| Value of trading portfolio realized |
|
|
$ 1.4 |
$ (0.3) |
|
| Not Designated as Hedging Instrument [Member] | Heating Oil [Member] |
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| Derivative [Line Items] |
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| Derivative, average price risk option strike price |
3.13 |
|
|
|
|
| Not Designated as Hedging Instrument [Member] | Heating Oil [Member] | Scenario, Forecast [Member] |
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| Derivative [Line Items] |
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|
|
|
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| Derivative, average price risk option strike price |
|
|
|
1.92 |
|
| Not Designated as Hedging Instrument [Member] | Diesel Purchases [Member] |
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| Derivative [Line Items] |
|
|
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| Percent of expected requirements covered |
86.00% |
|
|
|
|
| Not Designated as Hedging Instrument [Member] | Diesel Purchases [Member] | Scenario, Forecast [Member] |
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| Derivative [Line Items] |
|
|
|
|
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| Percent of expected requirements covered |
|
|
37.00% |
60.00% |
|
| Not Designated as Hedging Instrument [Member] | Diesel Purchases [Member] | Heating Oil [Member] |
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| Derivative [Line Items] |
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|
|
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| Quantities under derivative contracts |
66,000,000 |
|
|
|
|
| Not Designated as Hedging Instrument [Member] | Diesel Purchases [Member] | Heating Oil [Member] | Scenario, Forecast [Member] |
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| Derivative [Line Items] |
|
|
|
|
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| Quantities under derivative contracts |
|
|
|
19,500,000 |
|
| Not Designated as Hedging Instrument [Member] | Diesel Purchases [Member] | Minimum [Member] |
|
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| Derivative [Line Items] |
|
|
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| Gallons of diesel fuel purchased annually |
57,000,000 |
|
|
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|
| Not Designated as Hedging Instrument [Member] | Diesel Purchases [Member] | Maximum [Member] |
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| Derivative [Line Items] |
|
|
|
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| Gallons of diesel fuel purchased annually |
67,000,000 |
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