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Supplemental Information On Oil And Gas Exploration And Production Activities (Unaudited) - Changes In Standardized Measure Of Discontinued Future Net Cash Flows Relating To Proved Oil And Natural Gas Reserves (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Extractive Industries [Abstract]    
Standardized Measure, beginning of year $ 592,700 $ 85,883
Sales of oil and gas produced, net of production costs (136,143) (81,926)
Sales of minerals in place (41,320) (15,553)
Net changes in prices and production costs 319,486 155,629
Extensions, discoveries, and improved recoveries 185,540 201,801
Changes in income taxes, net (43,108) (5,941)
Previously estimated development costs incurred during the period 153,161 76,447
Net changes in future development costs (316,765) (168,940)
Purchases of minerals in place 57,013 244,785
Revisions of previous quantity estimates 144,356 68,705
Accretion of discount 51,222 28,985
Changes in timing of estimated cash flows and other (6,690) 2,825
Standardized Measure, end of year 959,452 592,700
Standardized measure of discounted future net cash flows attributable to noncontrolling interests $ 530,200 $ 336,100