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Derivative Instruments The Effect of Derivative Instruments on the Consolidated Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Cash Paid in Settlement of Commodity Derivative Instruments:	$ (16,991)	$ (47,103)
Unrealized Gain (Loss) on Commodity Derivative Instruments:	52,078	24,640
Gain (Loss) on Commodity Derivative Instruments	35,087	(22,463)
Basis Swap [Member]
Derivative [Line Items]
Cash Paid in Settlement of Commodity Derivative Instruments:	(16,557)	(21,280)
Unrealized Gain (Loss) on Commodity Derivative Instruments:	49,278	(139,111)
Gain (Loss) on Commodity Derivative Instruments	32,721	(160,391)
Natural Gas [Member] | Commodity Swaps [Member]
Derivative [Line Items]
Cash Paid in Settlement of Commodity Derivative Instruments:	(434)	(24,607)
Unrealized Gain (Loss) on Commodity Derivative Instruments:	2,800	162,604
Gain (Loss) on Commodity Derivative Instruments	2,366	137,997
Propane [Member] | Commodity Swaps [Member]
Derivative [Line Items]
Cash Paid in Settlement of Commodity Derivative Instruments:	0	(1,216)
Unrealized Gain (Loss) on Commodity Derivative Instruments:	0	1,147
Gain (Loss) on Commodity Derivative Instruments	$ 0	$ (69)

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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

Gain (loss) incurred in hedging activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

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- Definition

The difference between the book value and the sale price of agreements to purchase or sell mineral resources, energy, and agricultural products at some future point. This element refers to the gain (loss) included in earnings and not to the cash proceeds.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open derivatives, commodity, or energy contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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