Annual report pursuant to Section 13 and 15(d)

SUPPLEMENTAL OIL AND GAS INFORMATION (UNAUDITED) - Future Net Cash Flows of Proved Reserves (Details)

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SUPPLEMENTAL OIL AND GAS INFORMATION (UNAUDITED) - Future Net Cash Flows of Proved Reserves (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Extractive Industries [Abstract]        
Future Cash Inflows $ 3,395,670 $ 7,059,586 $ 7,524,587  
Future Production Costs (1,747,325) (2,868,762) (2,605,279)  
Future Development Costs (416,507) (855,041) (784,615)  
Future Income Tax Expense (3,273) (320,528) (611,989)  
Future Net Cash Inflows 1,228,565 3,015,255 3,522,704  
10% Annual Discount for Estimated Timing of Cash Flows (516,554) (1,337,194) (1,643,061)  
Standardized Measure of Discounted Future Net Cash Flows $ 712,011 $ 1,678,061 $ 1,879,643 $ 753,986