Acquisition and Disposition of Properties - Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenues	$ 168,326	$ 271,006	$ 390,184	$ 568,437
Loss from continuing operations	(111,601)	(3,154)	(127,021)	12,493
Net Income (Loss)	$ (111,601)	$ (7,953)	$ (127,021)	$ 45,363
Diluted earnings per average common share from continuing operations	$ (1.52)	$ (0.04)	$ (1.74)	$ 0.17
Diluted earnings per average common share	(1.52)	(0.11)	(1.74)	0.62
Basic earnings per average common share from continuing operations	(1.52)	(0.04)	(1.74)	0.17
Basic earnings per average common share	$ (1.52)	$ (0.11)	$ (1.74)	$ 0.62
San Juan Basin | Pro Forma
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenues	$ 167,734	$ 221,642	$ 357,578	$ 464,732
Loss from continuing operations	(110,362)	(13,769)	(149,203)	(11,920)
Net Income (Loss)	$ (110,362)	$ (18,568)	$ (149,203)	$ 20,950
Diluted earnings per average common share from continuing operations	$ (1.50)	$ (0.19)	$ (2.04)	$ (0.16)
Diluted earnings per average common share	(1.50)	(0.25)	(2.04)	0.29
Basic earnings per average common share from continuing operations	(1.50)	(0.19)	(2.04)	(0.16)
Basic earnings per average common share	$ (1.50)	$ (0.25)	$ (2.04)	$ 0.29