Acquisitions (Details) $ / shares in Units, $ in Thousands, shares in Millions				3 Months Ended	9 Months Ended	12 Months Ended			15 Months Ended
		Dec. 21, 2016 USD ($) shares	Oct. 04, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) a $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) $ / shares
Business Acquisition [Line Items]
Payments to acquire oil and gas property and equipment						$ 89,896	$ 2,183,790	$ 7,984
Carrying value of properties exchanged						293,963	733	$ 0
Wells in progress						321,347	235,147		$ 321,347
Proved oil and gas properties						6,139,379	5,700,418		6,139,379
Unproved oil and gas properties						$ 2,047,203	$ 2,471,947		$ 2,047,203
Common Stock, par value per share | $ / shares						$ 0.01	$ 0.01		$ 0.01
Other Howard and Martin Counties acquisitions 2017 [Member]
Business Acquisition [Line Items]
Net acres acquired | a						3,600
Payments to acquire oil and gas property and equipment						$ 76,500
QStar Acquisition 2016 [Member]
Business Acquisition [Line Items]
Payments to acquire oil and gas property and equipment		$ 1,200,000		$ 7,300	$ 1,174,628
Wells in progress		21,812
Proved oil and gas properties		61,239
Unproved oil and gas properties		1,538,264
Working capital acquired		(1,852)
Asset retirement obligations		$ (7,641)
Acquisition of oil and gas properties, consideration paid					$ 1,600,000
Private issuance of Common Stock for an acquisition | shares		13.4
Fair value of equity consideration	[1]	$ 437,194
Total consideration		1,611,822
Total oil and gas properties acquired		$ 1,621,315
Rock Oil Acquisition 2016 [Member]
Business Acquisition [Line Items]
Payments to acquire a business, gross			$ 991,000			$ 7,700			$ 998,691
Wells in progress			5,672
Proved oil and gas properties			82,584
Unproved oil and gas properties			913,819
Other assets			5,338
Total fair value of oil and gas properties acquired			1,007,413
Working capital acquired			(1,127)
Asset retirement obligations			(7,595)
Total fair value of net assets acquired			$ 998,691
Other Howard and Martin Counties trades [Member]
Business Acquisition [Line Items]
Non-monetary trade, acreage acquired | a						8,125
Non-monetary trade, acreage exchanged | a						7,580
Carrying value of properties exchanged						$ 294,000

[1] The Company issued approximately 13.4 million shares of common stock, par value $0.01 per share, in a private placement to the sellers in the QStar Acquisition on December 21, 2016. The equity consideration was valued on this date using Level 1 and Level 2 inputs with a discount applied due to the lack of marketability in the near term in accordance with the Lock-Up and Registration Rights Agreement that prohibited the sale of such stock until no earlier than the 90th day after issuance.