OIL AND NATURAL GAS OPERATIONS (Unaudited) - Standardized Measure of Discounted Future Net Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves, Standardized Measure [Abstract]
Future gross revenues				$ 15,531,237	$ 9,191,808	$ 11,714,729
Future production costs				4,467,989	3,126,153	4,353,974
Future development costs				2,077,918	1,632,577	1,961,661
Future income tax expense				1,381,999	762,921	1,065,887
Future net cash flows				7,603,331	3,670,157	4,333,207
Discount at 10% per annum				4,283,536	2,320,350	2,299,859
Standardized measure of discounted future net cash flows relating to proved oil and natural gas reserves	$ 1,349,807	$ 2,033,348	$ 4,219,656	$ 3,319,795	$ 1,349,807	$ 2,033,348
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flow Relating to Proved Oil and Gas Reserves [Roll Forward]
Balance at beginning of year	1,349,807	2,033,348	4,219,656
Revisions to reserves proved in prior years:
Net changes in prices and production costs	659,802	(343,839)	(3,101,283)
Net changes in future development costs	(86,642)	122,200	239,692
Net changes due to revisions in quantity estimates	389,684	(167,188)	(404,708)
Development costs incurred, previously estimated	148,534	71,099	350,560
Accretion of discount	149,664	203,335	542,105
Changes in timing and other	257,523	(100,742)	(1,024,114)
Total revisions	1,518,565	(215,135)	(3,397,748)
New field discoveries and extensions, net of future production and development costs	1,492,562	352,358	776,315
Sales of oil and gas produced, net of production costs	(788,130)	(440,446)	(514,380)
Purchases	3,769	1,733	8
Sales	0	(235,222)	(372,039)
Net change in income taxes	(256,778)	(146,829)	1,321,536
Net change in standardized measure of discounted future net cash flows	1,969,988	(683,541)	(2,186,308)
Balance at end of year	$ 3,319,795	$ 1,349,807	$ 2,033,348