Acquisition and Disposition of Properties - Pro Forma (Details) - Pro Forma - Permian Basin - Disposal group - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenues	$ 103,044	$ 160,942	$ 228,106	$ 376,582
Net Income (Loss)	$ (66,758)	$ (104,664)	$ (269,058)	$ (118,817)
Diluted earnings per average common share (in dollars per share)	$ (0.69)	$ (1.42)	$ (2.93)	$ (1.62)
Basic earnings per average common share (in dollars per share)	$ (0.69)	$ (1.42)	$ (2.93)	$ (1.62)