Discontinued Operations and Held for Sale Properties (Additional Information) (Details) $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended
	Sep. 02, 2014 USD ($)	Oct. 31, 2013 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2013 USD ($) MMBoe MBbls MMcf	Dec. 31, 2015 USD ($) MMBoe MBbls MMcf	Dec. 31, 2014 USD ($) MMBoe MBbls MMcf	Dec. 31, 2013 USD ($) MMBoe MBbls MMcf	Feb. 16, 2016 MMBoe	Mar. 31, 2014 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (BOE) | MMBoe				259.8	184.0	264.5	259.8
Gain on disposal of discontinued operations, net						$ 724,594	$ 5,605
Assets impairments from discontinued operations					$ 0	$ 1,936	$ 29,794
Natural Gas Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume) | MMcf				623,305	236,112	589,074	623,305
Oil Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume) | MBbls				113,795	108,319	118,697	113,795
Black Warrior Basin | Natural Gas Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume) | MMcf				97,000			97,000
Alabama Gas Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal group, consideration	$ 1,600,000
Debt assumed	267,000
Proceeds from sale	1,320,000
Gain on disposal of discontinued operations, net	$ 726,500
Black Warrior Basin | Alabama
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash received from sale of oil properties		$ 160,000
Gain on sale of oil and gas property				$ 35,000
North Louisiana/East Texas
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales price									$ 30,300
Assets impairments from discontinued operations					$ 0	$ 1,936	$ 29,794
North Louisiana/East Texas | Natural Gas Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume) | MMcf						23,000
North Louisiana/East Texas | Oil Reserves
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (volume) | MBbls						91
San Juan Basin properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (BOE) | MMBoe					16.930	69.038
Cash received from sale of oil properties			$ 384,000
Subsequent Event | Delaware Basin
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proved developed reserves at end of period (BOE) | MMBoe								25.200