SUPPLEMENTAL INFORMATION - NATURAL GAS AND CRUDE OIL PROPERTIES Standardized Measure of Discounted Future Cash Flows Relating to Proved Reserves (Unaudited) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) bbl	Dec. 31, 2016 USD ($) bbl	Dec. 31, 2015 USD ($) bbl
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place | bbl	(1,900,000)	(1,725,000)	(34,000)
Future Estimated Cash Flows	$ 12,340,407	$ 7,122,525	$ 6,297,298
Future Estimated Production Costs	(3,245,627)	(1,624,167)	(1,493,040)
Future Estimated Development Costs	(2,893,335)	(2,219,914)	(2,036,685)
Future Estimated Income Tax Expense	(748,494)	(597,476)	(508,332)
Future Net Cash Flows	5,452,951	2,680,968	2,259,241
10% Annual Discount for Estimated Timing of Cash Flows	(2,572,846)	(1,260,339)	(1,162,377)
Standardized Measure of Disconted Future Estimated Net Cash Flows	$ 2,880,105	$ 1,420,629	$ 1,096,864
Crude Oil [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place | bbl	(653,000)	(601,000)	(12,000)