Asset Impairment (Additional Information) (Details) $ in Thousands	1 Months Ended	3 Months Ended							12 Months Ended
	Oct. 31, 2013 USD ($)	Dec. 31, 2015 USD ($) MMBoe MBbls MMcf	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) MMBoe MBbls MMcf	Sep. 30, 2014 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 ($) MMBoe MBbls MMcf	Mar. 31, 2014 USD ($)
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment									$ 1,292,308	$ 416,801	$ 13,906
Price curve, term									5 years
Increase (decrease) in commodity price assumptions (percent)									3.00%
Proved developed reserves at end of period (BOE) | MMBoe		184.0				264.5		259.8	184.0	264.5	259.8
Assets impairments from discontinued operations									$ 0	$ 1,936	$ 29,794
Central Basin Platform
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment									484,848	0	0
San Juan Basin properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment									$ 133,055	$ 230,315	0
Proved developed reserves at end of period (BOE) | MMBoe		16.930				69.038			16.930	69.038
Cash received from sale of oil properties					$ 384,000
San Juan Basin properties | Discontinued Operations, Held-for-sale or Disposed of by Sale
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment						$ 88,100	$ 142,200
San Juan Proved and Unproved Properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		$ 133,100
Permian Basin Unproved Leasehold Properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment						55,100			$ 29,168	$ 64,361	13,906
San Juan Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment									37,934	5,755	0
Midland Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment							$ 25,800		0	25,776	0
Delaware Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment						$ 90,600			607,303	90,594	0
North Louisiana/East Texas
Impaired Long-Lived Assets Held and Used [Line Items]
Sales price												$ 30,300
Assets impairments from discontinued operations									$ 0	$ 1,936	$ 29,794
Natural Gas
Impaired Long-Lived Assets Held and Used [Line Items]
Increase (decrease) in commodity price assumptions (percent)			(6.00%)	(12.00%)
Proved developed reserves at end of period (volume) | MMcf		236,112				589,074		623,305	236,112	589,074	623,305
Natural Gas | North Louisiana/East Texas
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves at end of period (volume) | MMcf						23,000				23,000
Oil Reserves
Impaired Long-Lived Assets Held and Used [Line Items]
Increase (decrease) in commodity price assumptions (percent)			(12.00%)	(19.00%)
Proved developed reserves at end of period (volume) | MBbls		108,319				118,697		113,795	108,319	118,697	113,795
Oil Reserves | Permian Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		$ 646,100	$ 390,200		$ 4,300				$ 1,092,200
Oil Reserves | Central Basin Platform
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment				$ 51,500
Oil Reserves | North Louisiana/East Texas
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves at end of period (volume) | MBbls						91				91
Alabama | Black Warrior Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Cash received from sale of oil properties	$ 160,000
Gain on sale of oil and gas property								$ 35,000
Black Warrior Basin | Natural Gas
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves at end of period (volume) | MMcf								97,000			97,000