Derivative maturity month year.

No definition available.

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Balance Type:	na
Period Type:	duration

- Definition

Value of input used to measure net derivative asset (liability).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

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Period Type:	instant

- Definition

The average forward price on the group of price risk forward or futures contracts, such as gas futures contracts.

+ References

No definition available.

+ Details

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Period Type:	instant

- 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.

+ Details

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Period Type:	duration

- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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Natural Gas Derivative Instruments - Additional Information (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) $ / MMBTU	Sep. 30, 2017 USD ($) $ / MMBTU	Sep. 30, 2018 USD ($) MMBTU $ / MMBTU	Sep. 30, 2017 USD ($) $ / MMBTU
Natural gas derivative contract
Derivative [Line Items]
Last derivative contract expiration month and year			2018-12
Contracts volume, derivative instruments \| MMBTU			450,000
Average price \| $ / MMBTU	2.90	3.00	2.90	3.00
Natural gas derivative contract \| 2015 through December 31, 2018
Derivative [Line Items]
Contracts volume, derivative instruments \| MMBTU			480,000
Average price \| $ / MMBTU	4.31		4.31
Natural gas derivative contract \| Measurement Input, Discount Rate
Derivative [Line Items]
Estimated cash flows, discount rate	8.0		8.0
Cost of Sales
Derivative [Line Items]
Gain (loss) on derivative instruments \| $	$ 217	$ 285	$ 847	$ (916)