Asset Impairment - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 0		$ 60,413		$ 220,025	$ 66,996
Price curve, term					5 years
Increase (decrease) in carrying amount of properties, percent					3.00%
Oil
Impaired Long-Lived Assets Held and Used [Line Items]
Increase (decrease) in carrying amount of properties, percent		(5.00%)
Natural Gas
Impaired Long-Lived Assets Held and Used [Line Items]
Increase (decrease) in carrying amount of properties, percent		(4.00%)
Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		$ 208,300	51,500	$ 4,300
Permian Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0	4,100	8,939		$ 4,135	10,944
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0	$ 7,500	0		7,519	0
San Juan Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 0		$ 0		$ 40	$ 248