Acquisition and Disposition of Properties - Held for Sale Properties by Major Classes of Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Oil and natural gas properties	$ 571,535
Less accumulated depreciation, depletion and amortization	(388,301)
Total assets held for sale	183,234
Other long-term liabilities	(14,102)
Total liabilities held for sale	(14,102)	$ (12,789)
Total net assets held for sale	169,132
Permian Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Oil and natural gas properties	260,253
Less accumulated depreciation, depletion and amortization	(166,254)
Total assets held for sale	93,999
Other long-term liabilities	(1,086)
Total liabilities held for sale	(1,086)
Total net assets held for sale	92,913
San Juan Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Inventories		3,651
Oil and natural gas properties	311,282	305,386
Less accumulated depreciation, depletion and amortization	(222,047)	(219,059)
Other property and equipment, net		3,761
Total assets held for sale	89,235	93,739
Other long-term liabilities	(13,016)	(12,789)
Total liabilities held for sale	(13,016)	(12,789)
Total net assets held for sale	$ 76,219	$ 80,950