The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
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The current portion of money or property received from customers which is either to be returned upon satisfactory contract completion or applied to customer receivables in accordance with the terms of the contract or the understandings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Aggregate net fair value of all derivative instruments designated as hedging instruments. Includes instruments designated as cash flow hedges, fair value hedges, and hedges of net investments in foreign operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611

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-Topic 825
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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.

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No definition available.

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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.

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No definition available.

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The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)(1)
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The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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-Subparagraph (SX 210.5-02.8,17)
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Derivatives, Hedging Programs and Other Financial Instruments, Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Debt Instrument, Term		12 months
Derivative Instruments in Hedges, at Fair Value, Net	$ 19,100,000	$ 19,100,000					$ 4,000,000
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months		500,000
Margin Deposit Assets	0	0					$ 0
Customer Deposits, Current	0	0
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	$ 0	$ 0
Scenario, Forecast \| Natural Gas Member
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage			39.00%	71.00%	71.00%	72.00%
Scenario, Forecast \| Electricity Member
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage			18.00%	55.00%	55.00%	54.00%