Annual report pursuant to Section 13 and 15(d)

SUPPLEMENTAL OIL AND GAS INFORMATION (UNAUDITED) - Standardized Measure of Discounted Future Net Cash Flows (Details)

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SUPPLEMENTAL OIL AND GAS INFORMATION (UNAUDITED) - Standardized Measure of Discounted Future Net Cash Flows (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Increase (Decrease) in Standardized Measure of Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Roll Forward]      
Beginning of Period $ 1,678,061 $ 1,879,643 $ 753,986
Sales of Oil and Natural Gas Produced, Net of Production Costs (177,932) (424,548) (381,961)
Extensions and Discoveries 52,232 282,528 549,353
Previously Estimated Development Cost Incurred During the Period 78,633 100,987 115,542
Net Change of Prices and Production Costs (815,278) (680,119) 484,122
Change in Future Development Costs (150,991) (174,729) (91,829)
Revisions of Quantity and Timing Estimates (280,481) (226,721) 66,185
Accretion of Discount 182,202 218,023 75,800
Change in Income Taxes 143,438 156,621 (296,571)
Purchases of Minerals in Place 0 338,289 502,193
Other 2,127 208,087 19,902
End of Period $ 712,011 $ 1,678,061 $ 1,879,643