OIL AND NATURAL GAS OPERATIONS (Unaudited) - Results of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserve Quantities [Line Items]
Gross revenues	$ 961,045	$ 532,889	$ 878,554
Production (lifting costs)	243,144	214,652	285,760
Exploration expense	10,075	5,415	14,877
Depreciation, depletion and amortization including asset impairments	480,491	663,659	1,880,190
Accretion expense	5,831	6,672	7,108
Income tax expense (benefit)	79,815	(123,153)	(469,362)
Results of operations from producing activities	141,689	(234,356)	(840,019)
Commodity contracts
Reserve Quantities [Line Items]
Open non-cash mark-to-market losses on derivative instruments	$ 10,759	$ 71,190	$ 281,752