Asset Impairment - Additional Information (Details) bbl in Thousands, $ in Thousands, Mcf in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2013 Mcf bbl
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 60,413	$ 1,342		$ 66,996	$ 2,588
Permian Basin and San Juan Basin [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	8,900			11,200
Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	8,939	1,339		10,944	2,587
Permian Basin | Oil
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	51,474	0		55,804	0
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 0	$ 3		$ 248	$ 1
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
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