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Acquisitions and Divestitures - Acquisitions (Details) a in Thousands, $ in Thousands				3 Months Ended									12 Months Ended
	Jul. 01, 2015 USD ($)	Oct. 01, 2013 USD ($) a seller	Sep. 26, 2013 USD ($) a	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Business Acquisition [Line Items]
Revenues				$ 182,067	$ 197,235	$ 230,046	$ 180,387	$ 299,672	$ 368,659	$ 372,378	$ 349,519		$ 789,735	$ 1,390,228	$ 1,141,999
Operating income (loss)				$ (53,166)	$ (19,926)	$ (7,437)	$ (33,635)	$ 15,924	$ 134,103	$ 166,545	$ 329,080		$ (114,164)	$ 645,652	$ 504,398
West Williston
Business Acquisition [Line Items]
Number of sellers | seller		2
Acres acquired | a		136
Consideration transferred		$ 1,475,361
Recognized identifiable assets acquired		$ 1,475,361
Revenues												$ 57,600
Operating income (loss)												14,900
Acquisition costs												$ 2,000
East Nesson
Business Acquisition [Line Items]
Acres acquired | a			25
Consideration transferred			$ 56,750
Recognized identifiable assets acquired			56,750
Capital spending commitment			$ 8,200
Payment to seller for remaining committed amount for drilling and completion activities	$ 3,200

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