Derivatives and Financial Instruments - Changes in Fair Value of Company's Commodity Derivative Instruments (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivatives not designated as hedging instruments
Gain (loss) on commodity derivative instruments	$ 22,003	$ (30,733)	$ 44,728	$ (20,107)
Net cash received on settlements of derivative instruments			(7,359)	(33,918)
Not Designated as Hedging Instrument
Derivatives not designated as hedging instruments
Beginning fair value of commodity derivative instruments			(16,719)	64,534
Net change in fair value of commodity derivative instruments			37,369	(54,025)
Ending fair value of commodity derivative instruments	$ 20,650	$ 10,509	20,650	10,509
Oil \| Not Designated as Hedging Instrument
Derivatives not designated as hedging instruments
Gain (loss) on commodity derivative instruments			27,799	(12,615)
Net cash received on settlements of derivative instruments			(6,656)	(18,766)
Natural Gas \| Not Designated as Hedging Instrument
Derivatives not designated as hedging instruments
Gain (loss) on commodity derivative instruments			16,929	(7,492)
Net cash received on settlements of derivative instruments			$ (703)	$ (15,152)

The net cash outflow or inflow from derivative instruments during the period

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- Definition

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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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=64837297&loc=SL5618551-113959

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open agreements to purchase or sell mineral resources, energy, and agricultural products at some future point 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=66902209&loc=d3e3602-108585

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