SUPPLEMENTAL OIL AND GAS DISCLOSURES (Unaudited) (Capitalized Costs Relating to Oil and Natural Gas Producing Activities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Capitalized Costs, Oil and Gas Producing Activities, Net [Abstract]
Proved properties	$ 2,239,444	$ 2,110,346
Unproved properties	813,310	816,282
Total	3,052,754	2,926,628
Accumulated depreciation, depletion, amortization and impairment	(2,837,402)	(2,163,291)
Net capitalized costs	$ 215,352	$ 763,337