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- Definition

Fair Value Assumptions, Escalation Factor

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- Definition

Fair Value Assumptions, Operation And Maintenance Charges

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- Definition

The forward price on the price risk forward or futures contract, such as a gas futures contract.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
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-Publisher FASB
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-Publisher FASB
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Nominal energy measure used to calculate payments on a derivative instrument.

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- Definition

Agreed upon price for the exchange of the underlying asset.

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-Topic 820
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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.

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Fair Value (Quantitative Information) (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / MWH MMBTU MWh $ / shares $ / MmBtu	Dec. 31, 2017 USD ($)
Power Exchange Agreements [Member] \| Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Average operation and maintenance charges \| $ / MWH	41.95
Minimum [Member] \| Power Exchange Agreements [Member] \| Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions Operation And Maintenance Charges \| $ / MWH	38.87
Transaction/Delivery Volumes \| MWh	42,682
Minimum [Member] \| Power Option Agreement [Member] \| Black Scholes Merton [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Transaction/Delivery Volumes \| MWh	94,221
Maximum [Member] \| Power Exchange Agreements [Member] \| Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions Operation And Maintenance Charges \| $ / MWH	45.20
Transaction/Delivery Volumes \| MWh	396,984
Maximum [Member] \| Power Option Agreement [Member] \| Black Scholes Merton [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Transaction/Delivery Volumes \| MWh	128,491
Fair Value, Measurements, Recurring [Member] \| Power Exchange Agreements [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Liability \| $	$ (10,163)	$ (13,245)
Fair Value, Measurements, Recurring [Member] \| Power Option Agreement [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Liability \| $	(5)	(19)
Fair Value, Measurements, Recurring [Member] \| Natural Gas Exchange Agreements [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative Liability \| $	$ (2,805)	$ (3,164)
Sales [Member] \| Minimum [Member] \| Natural Gas Exchange Agreements [Member] \| Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price \| $ / MmBtu	1.33
Transaction/Delivery Volumes \| MMBTU	60,000
Sales [Member] \| Maximum [Member] \| Natural Gas Exchange Agreements [Member] \| Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price \| $ / MmBtu	2.85
Transaction/Delivery Volumes \| MMBTU	310,000
Purchase [Member] \| Minimum [Member] \| Natural Gas Exchange Agreements [Member] \| Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price \| $ / MmBtu	1.41
Transaction/Delivery Volumes \| MMBTU	115,000
Purchase [Member] \| Maximum [Member] \| Natural Gas Exchange Agreements [Member] \| Internally Derived Weighted Average Cost Of Gas [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Derivative, Forward Price \| $ / MmBtu	2.00
Transaction/Delivery Volumes \| MMBTU	310,000
2019 \| Power Option Agreement [Member] \| Black Scholes Merton [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Exercise Price \| $ / shares	$ 40.42
2018 to 2019 [Member] \| Power Exchange Agreements [Member] \| Surrogate Facility Pricing [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Escalation Factor	5.00%
2018 \| Power Option Agreement [Member] \| Black Scholes Merton [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Assumptions, Exercise Price \| $ / shares	$ 34.01