EXPLORATORY COSTS - Capitalized Exploratory Well Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) well	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Capitalized exploratory well costs at beginning of period	$ 164,996	$ 103,588	$ 119,439
Additions pending determination of proved reserves	666,282	344,045	634,908
Reclassifications due to determination of proved reserves	(699,078)	(282,637)	(650,759)
Capitalized exploratory well costs at end of period	132,200	164,996	$ 103,588
Capitalized Exploratory Well Costs [Abstract]
Exploratory wells in progress (drilling rig not released)	10,879	14,531
Capitalized exploratory well costs for a period of one year or less	121,321	143,602
Capitalized exploratory well costs for a period greater than one year	0	6,863
Total capitalized exploratory well costs	$ 132,200	$ 164,996
Wells in process of drilling | well	49
Number of wells capitalized for a period greater than one year | well	0