OIL AND NATURAL GAS OPERATIONS (Unaudited) - Oil and Gas Operations, Activities (Details) - MMBoe	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserve Quantities [Line Items]
Reserves included in engineer estimates (in percentage)	99.00%
Revisions of previous estimates (in mmboe)	39.8	(26.0)	(58.9)
Purchases (in mmboe)	0.2	0.1	0.0
Extensions and discoveries (in mmboe)	115.5	64.1	132.6
Percentage of undeveloped portion of proved reserves	27.00%	65.00%	78.00%
Percentage of developed portion of proved reserves	73.00%	35.00%	22.00%
Sales (in mmboe)		55.0	67.7
Extension Drilling
Reserve Quantities [Line Items]
Extensions and discoveries (in mmboe)	0.6		3.1
Exploratory Drilling
Reserve Quantities [Line Items]
Extensions and discoveries (in mmboe)	114.9	64.1	129.5
Change in year-end pricing revisions
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)	11.6	(10.6)	(38.0)
Well performance revisions
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)	12.0
Extending lateral length revisions
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)	17.6	7.5
Changes in plant yield revisions
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)	3.0
No longer expected to be drilled in five years
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)		(22.9)
No longer expected to be drilled beyond five years
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)	(4.6)
Expected to be drilled beyond five years
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)			(8.2)
Declines in Wolfberry Wells
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)			(5.5)
Interference caused by our wellborne placement geometry
Reserve Quantities [Line Items]
Revisions of previous estimates (in mmboe)			(5.0)