Acquisition and Disposition of Properties - Pro Forma (Details) - Pro Forma - Permian and San Juan Basin - Disposal group - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenues	$ 182,223	$ 275,813	$ 388,603	$ 597,253
Net Income (Loss)	$ (5,899)	$ (219,605)	$ (252,664)	$ (354,409)
Diluted earnings per average common share (in dollars per share)	$ (0.06)	$ (2.79)	$ (2.70)	$ (4.72)
Basic earnings per average common share (in dollars per share)	$ (0.06)	$ (2.79)	$ (2.70)	$ (4.72)