Asset Impairment - Summary of Impairments Recognized (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 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
Central Basin Platform
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0		51,474	187,043	51,474
Delaware Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0		0	21,288	4,330
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0	$ 7,500	0	7,519	0
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 unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 0		$ 0	$ 40	$ 248