Gallons of diesel fuel purchased annually.

No definition available.

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- Definition

Value of trading portfolio realized at a certain point in time gains (losses)

+ References

No definition available.

+ Details

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- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

The average strike price on the group of price risk option contracts such as put options or call options.

+ References

No definition available.

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- Definition

Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=d3e41678-113959

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226016-175313

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.

+ References

No definition available.

+ Details

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- Definition

Amount of gain (loss) resulting from the difference between the acquisition price and the selling price or fair value of trading assets and trading liabilities, conducted separately from customer trading activities. Includes, but is not limited to, changes in fair value of trading assets and trading liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(e))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 320
-Section 35
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-Name Accounting Standards Codification
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-SubTopic 320
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42567-110969

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4F
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624186-113959

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Derivatives (Narrative) (Details) gal in Millions, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) gal $ / option	Mar. 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 $ / option	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Current liability for the obligation to return cash collateral \| $	$ 4.8				$ 2.8
Net unrealized and realized gains (losses) related to trading portfolio \| $	$ (0.7)	$ 0.1
Scenario, Forecast [Member]
Derivative [Line Items]
Value of trading portfolio realized \| $			$ (0.6)
Not Designated as Hedging Instrument [Member] \| Heating Oil [Member]
Derivative [Line Items]
Percent of expected requirements covered	75.00%
Derivative, average price risk option strike price (in usd per gallon) \| $ / option	1.77
Not Designated as Hedging Instrument [Member] \| Diesel Purchases [Member] \| Scenario, Forecast [Member]
Derivative [Line Items]
Percent of expected requirements covered				12.00%
Derivative, average price risk option strike price (in usd per gallon) \| $ / option				1.92
Not Designated as Hedging Instrument [Member] \| Diesel Purchases [Member] \| Heating Oil [Member]
Derivative [Line Items]
Quantities under derivative contracts (in gallons) \| gal	30
Not Designated as Hedging Instrument [Member] \| Diesel Purchases [Member] \| Minimum [Member]
Derivative [Line Items]
Gallons of diesel fuel purchased annually \| gal	38
Not Designated as Hedging Instrument [Member] \| Diesel Purchases [Member] \| Maximum [Member]
Derivative [Line Items]
Gallons of diesel fuel purchased annually \| gal	44