Derivative Instruments - The Effect of Derivative Instruments on the Consolidated Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Cash Received (Paid) in Settlement of Commodity Derivative Instruments:	$ 57,041	$ 2,825	$ 26,331	$ 2,518
Unrealized Gain (Loss) on Commodity Derivative Instruments:	156,872	15,180	213,787	76,234
Gain (Loss) on Commodity Derivative Instruments:	213,913	18,005	240,118	78,752
Natural Gas \| Commodity Member
Derivative [Line Items]
Cash Received (Paid) in Settlement of Commodity Derivative Instruments:	61,441	6,916	53,058	23,540
Unrealized Gain (Loss) on Commodity Derivative Instruments:	126,617	27,749	302,701	76,999
Gain (Loss) on Commodity Derivative Instruments:	188,058	34,665	355,759	100,539
Natural Gas \| Basis Swap
Derivative [Line Items]
Cash Received (Paid) in Settlement of Commodity Derivative Instruments:	(4,400)	(4,091)	(26,727)	(21,022)
Unrealized Gain (Loss) on Commodity Derivative Instruments:	30,255	(12,569)	(88,914)	(765)
Gain (Loss) on Commodity Derivative Instruments:	$ 25,855	$ (16,660)	$ (115,641)	$ (21,787)

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.

No definition available.

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- Definition

Gain (loss) incurred in hedging activities.

+ 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

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&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

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