ASSET IMPAIRMENT - Summary of Impairments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		$ 1,671	$ 220,652	$ 1,292,308
Central Basin Platform
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		1,096	187,043	484,848
Delaware Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		0	21,288	607,303
Midland Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		0	0	0
San Juan Basin properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 7,500	0	7,519	133,055
Permian Basin Unproved Leasehold Properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		575	4,762	29,168
San Juan Basin unproved leasehold properties
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment		$ 0	$ 40	$ 37,934