Acquisition and Disposition of Properties - Held for Sale Properties by Major Classes of Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total liabilities held for sale	$ 0	$ (12,789)
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		305,386
Less accumulated depreciation, depletion and amortization		(219,059)
Other property and equipment, net		3,761
Total assets held for sale		93,739
Other long-term liabilities		(12,789)
Total liabilities held for sale		(12,789)
Total net assets held for sale		$ 80,950