Discontinued Operations and Held for Sale Properties - Additional Information (Details) bbl in Thousands, $ in Thousands, Mcf in Millions		3 Months Ended			9 Months Ended
	Sep. 02, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2013 Mcf bbl
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on disposal of discontinued operations			$ 726,410			$ 724,743
Impairment of oil and gas properties held-for-sale		$ 0	0		$ 0	1,667
Alabama Gas Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Amount of consideration received	$ 1,600,000
Amount of debt assumed	267,000
Proceeds from sale	1,320,000
Loss on disposal of discontinued operations	$ 726,500
North Louisiana and East Texas Natural Gas and Oil Properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale price of gas and oil properties				$ 30,300
Impairment of oil and gas properties held-for-sale		$ 0	$ 0	$ 1,700	$ 0	$ 1,667
North Louisiana and East Texas Natural Gas and Oil Properties | Natural Gas
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves (volume) | Mcf							23
North Louisiana and East Texas Natural Gas and Oil Properties | Oil
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves (volume) | bbl							91