Represents the electricity forward price per Megawatt Hours, used as an input to measure fair value.

No definition available.

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- Definition

Represents the gas price per Metric Million British Thermal Units, used as an input to measure fair value.

+ References

No definition available.

+ Details

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- Definition

Represents the percentage of implied electricity volatilities.

+ References

No definition available.

+ Details

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- Definition

Represents the percentage of implied electricity natural gas price volatilities.

+ References

No definition available.

+ Details

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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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

Fair value of financial and nonfinancial obligations.

+ References

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- Definition

Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

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Fair Value Measurements - Level 3 Quantative Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2014 USD ($) $ / MMBTU $ / MWh	Dec. 31, 2013 USD ($)
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Assets	$ 30,364				$ 32,598				$ 30,364	$ 32,598
Liabilities	63,343				73,984				63,343	73,984
Operating revenues	734,430	$ 1,199,146	$ 890,648	$ 671,219	726,450	$ 1,172,667	$ 906,264	$ 686,251	3,495,443	3,491,632	$ 3,454,628
Electricity forward contracts
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Assets	24,543				29,471				24,543	29,471
Liabilities	54,679				55,894				$ 54,679	$ 55,894
Electricity forward contracts \| Minimum \| Discounted cash flows
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (per MWh) \| $ / MWh									15.92	19.51
Electricity forward contracts \| Maximum \| Discounted cash flows
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (per MWh) \| $ / MWh									40.73	56.72
Electricity forward contracts \| Weighted Average \| Discounted cash flows
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (per MWh) \| $ / MWh									26.86	35.27
Option Contracts
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Liabilities	5,628				15,035				$ 5,628	$ 15,035
Option Contracts \| Minimum \| Option model
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (per MWh) \| $ / MWh									23.87	32.14
Implied electricity price volatilities (as a percent)									40.00%	23.00%
Implied natural gas price volatilities (as a percent)									32.00%	23.00%
Natural gas forward price (per MMbtu) \| $ / MMBTU										3.18
Option Contracts \| Maximum \| Option model
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (per MWh) \| $ / MWh									44.13	66.09
Implied electricity price volatilities (as a percent)									59.00%	63.00%
Implied natural gas price volatilities (as a percent)									40.00%	41.00%
Natural gas forward price (per MMbtu) \| $ / MMBTU										3.29
Option Contracts \| Weighted Average \| Option model
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (per MWh) \| $ / MWh									33.91	45.83
Implied electricity price volatilities (as a percent)									52.00%	41.00%
Implied natural gas price volatilities (as a percent)									35.00%	31.00%
Natural gas forward price (per MMbtu) \| $ / MMBTU										3.25
Natural gas forward contracts
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Assets	5,821				3,127				$ 5,821	$ 3,127
Liabilities	$ 3,036				$ 3,055				$ 3,036	$ 3,055
Natural gas forward contracts \| Minimum \| Discounted cash flows
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Natural gas forward price (per MMbtu) \| $ / MMBTU									2.18	2.98
Natural gas forward contracts \| Maximum \| Discounted cash flows
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Natural gas forward price (per MMbtu) \| $ / MMBTU									3.14	4.13
Natural gas forward contracts \| Weighted Average \| Discounted cash flows
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Natural gas forward price (per MMbtu) \| $ / MMBTU										3.45
Natural gas forward contracts \| Weighted Average \| Option model
Information regarding the entity's internally developed significant unobservable inputs used to value its level 3 instruments
Electricity forward price (per MWh) \| $ / MWh									2.61