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Acquisitions and Divestitures - Acquisitions (Details) a in Thousands, $ in Thousands					3 Months Ended								12 Months Ended
	Dec. 08, 2017 shares	Dec. 01, 2017 USD ($) a	Apr. 25, 2017 USD ($)	Dec. 01, 2016 USD ($) a	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Acquisitions of oil and gas properties													$ 61,874	$ 781,522	$ 28,817
Total revenues					$ 404,469	$ 304,748	$ 254,091	$ 285,116	$ 217,991	$ 177,311	$ 179,080	$ 130,283	1,248,424	704,665	789,735
Operating income					$ 86,103	$ 32,394	$ 5,379	$ 20,092	$ (1,702)	$ (25,702)	$ (28,214)	$ (75,215)	143,968	(130,833)	(114,164)
Permian Basin Acquisition
Business Acquisition [Line Items]
Acquisitions of oil and gas properties		$ 549,800
Shares issued as consideration (shares) | shares	46,000,000
Acres acquired | a		22
MIdstream Assets Acquisition
Business Acquisition [Line Items]
Consideration transferred			$ 12,700
Installment notes payable			4,900
Fair value of assets acquired			$ 12,700
Williston Basin Acquisition
Business Acquisition [Line Items]
Consideration transferred				$ 764,300
Acres acquired | a				55
Recognized identifiable assets acquired				$ 764,300
Total revenues														14,600
Operating income														5,900
Acquisition costs														300
Forge Energy | Permian Basin Acquisition
Business Acquisition [Line Items]
Security Deposit		$ 47,300
Several Acreage and Producing Assets
Business Acquisition [Line Items]
Acquisitions of oil and gas properties													$ 6,100	$ 15,800	$ 28,817

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of assets acquired at the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Aggregate revenue during the period related to oil and gas business activities.

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