Asset Impairment - Additional Information (Details) bbl in Thousands, $ in Thousands, Mcf in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 MBoe	Dec. 31, 2013 Mcf bbl
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 399,394		$ 178,912		$ 466,390	$ 181,500
Price curve, term					5 years
Increase (decrease) in carrying amount of properties, percent					3.00%
Impairment of oil and gas properties held-for-sale	$ 0		0		$ 0	1,667
Oil
Impaired Long-Lived Assets Held and Used [Line Items]
Increase (decrease) in carrying amount of properties, percent	19.00%
Natural Gas
Impaired Long-Lived Assets Held and Used [Line Items]
Increase (decrease) in carrying amount of properties, percent	12.00%
Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment			31,000
Permian Basin | Oil
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 390,246				446,100
Central Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	371,593		0		423,067	0
Central Basin | Oil
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		$ 51,500
Permian Basin Unproved Leasehold Properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	9,148		5,231		20,092	7,818
Permian Basin and San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment					20,300
San Juan Proved and Unproved Properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment			147,900
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0		142,172		0	142,172
Proved developed reserves (MBOE) | MBoe							69,038
North Louisiana and East Texas Natural Gas and Oil Properties
Impaired Long-Lived Assets Held and Used [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
Discount rate				10.00%
North Louisiana and East Texas Natural Gas and Oil Properties | Oil
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves (volume) | bbl								91
North Louisiana and East Texas Natural Gas and Oil Properties | Natural Gas
Impaired Long-Lived Assets Held and Used [Line Items]
Proved developed reserves (volume) | Mcf								23