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Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Changes in Proved Undeveloped Reserves (Detail)
 12 Months Ended
Dec. 31, 2020
MMcfe
Extractive Industries [Abstract]  
Beginning proved undeveloped reserves at December 31, 2019 8,289,115
Undeveloped reserves transferred to developed (1,258,551)
Revisions (675,150) [1]
Sales (175,274)
Extension and discoveries 1,230,434
Ending proved undeveloped reserves at December 31, 2020 7,410,574
[1] Includes 961 Bcfe of proved undeveloped reserves removed and deferred due to the five-year rule which can be included in our future proved reserves as these locations are added back to our five-year development plan.