Asset Impairment - Summary of Impairments Recognized (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 587		$ 399,394	$ 220,612	$ 466,390
Central Basin Platform
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0		371,593	187,043	423,067
Delaware Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	0		18,653	21,288	22,983
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	587	$ 4,700	9,148	4,722	20,092
San Juan Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 0		$ 0	$ 40	$ 248