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Derivative Instruments (Net (Loss) Gain on Derivative Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative [Line Items]
Net (loss) gain on natural gas, oil, and NGL derivatives	$ (16,529)	$ 99,577
Natural gas derivatives
Derivative [Line Items]
Net (loss) gain on natural gas, oil, and NGL derivatives	(9,696)	86,277
Oil derivatives
Derivative [Line Items]
Net (loss) gain on natural gas, oil, and NGL derivatives	(9,147)	10,905
Natural gas liquids derivatives
Derivative [Line Items]
Net (loss) gain on natural gas, oil, and NGL derivatives	$ 2,314	$ 2,395

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- Definition

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

+ 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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