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

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 carrying amount of cash collateral received from hedge counterparties in support of energy risk management activities for which there is an offsetting liability within current liabilities. The Company does not have the right to pledge, invest, or use the cash collateral for general corporate purposes.

+ References

No definition available.

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- Definition

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.

+ References

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)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

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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=84234895&loc=d3e41678-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=82849420&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

Period remaining until the derivative contract matures, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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Derivative Instruments - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) MW	Dec. 31, 2016 USD ($) MW	Dec. 31, 2010 MW
Derivative [Line Items]
AOCL to be reclassified within 12 months	$ 6,400
Funds deposited by counterparty	34,436	$ 43,635
Counterparty deposit liability	$ 34,436	$ 43,635
Undesignated Derivative Instruments [Member] \| Energy derivative [Member]
Derivative [Line Items]
Nonmonetary notional amount \| MW	911,048	1,201,691	504,220
Minimum [Member] \| Designated as Hedging Instrument [Member] \| Interest rate swaps [Member]
Derivative [Line Items]
Derivative, Remaining Maturity	118 months
Minimum [Member] \| Undesignated Derivative Instruments [Member] \| Interest rate swaps [Member]
Derivative [Line Items]
Derivative, Remaining Maturity	46 months
Minimum [Member] \| Undesignated Derivative Instruments [Member] \| Foreign currency forward contracts [Member]
Derivative [Line Items]
Derivative, Remaining Maturity	2 months
Maximum [Member] \| Designated as Hedging Instrument [Member] \| Interest rate swaps [Member]
Derivative [Line Items]
Derivative, Remaining Maturity	231 months
Maximum [Member] \| Undesignated Derivative Instruments [Member] \| Interest rate swaps [Member]
Derivative [Line Items]
Derivative, Remaining Maturity	156 months
Maximum [Member] \| Undesignated Derivative Instruments [Member] \| Foreign currency forward contracts [Member]
Derivative [Line Items]
Derivative, Remaining Maturity	24 months