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Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Proved Developed and Undeveloped Reserves (Detail)
 12 Months Ended
Dec. 31, 2020
MMcfe
MMcf
MBbls
Dec. 31, 2019
MMcfe
MMcf
MBbls
Dec. 31, 2018
MMcfe
MMcf
MBbls
Proved undeveloped reserves:      
Proved undeveloped reserves | MMcfe 7,410,574 8,289,115  
Natural Gas      
Reserve Quantities [Line Items]      
Beginning Balance | MMcf 12,114,977 12,027,702 10,263,649
Revisions | MMcf (789,992) 33,122 178,595
Extensions, discoveries and additions | MMcf 1,007,415 959,901 2,269,427
Property sales | MMcf (609,311) (327,634) (135,884)
Production | MMcf (574,529) (578,114) (548,085)
Ending Balance | MMcf 11,148,560 12,114,977 12,027,702
Proved developed reserves:      
Proved developed reserves | MMcf 6,350,057 6,486,211 6,451,012
Proved undeveloped reserves:      
Proved undeveloped reserves | MMcf 4,798,503 5,628,766 5,576,690
NGLs      
Reserve Quantities [Line Items]      
Beginning Balance 938,236 921,594 763,264
Revisions 42,741 57,311 84,993
Extensions, discoveries and additions 38,298 26,505 128,436
Property sales (30,317) (28,324) (16,774)
Production (37,492) (38,850) (38,325)
Ending Balance 951,466 938,236 921,594
Proved developed reserves:      
Proved developed reserves 550,771 535,007 512,318
Proved undeveloped reserves:      
Proved undeveloped reserves 400,695 403,229 409,276
Crude Oil and Condensate      
Reserve Quantities [Line Items]      
Beginning Balance 74,532 85,856 69,854
Revisions (12,444) (12,320) 7,197
Extensions, discoveries and additions 4,512 7,057 17,309
Property sales (6,145) (2,371) (4,276)
Production (2,829) (3,690) (4,228)
Ending Balance 57,626 74,532 85,856
Proved developed reserves:      
Proved developed reserves 22,976 34,369 38,658
Proved undeveloped reserves:      
Proved undeveloped reserves 34,650 40,163 47,198
Natural Gas Equivalents      
Proved developed reserves:      
Proved developed reserves | MMcfe [1] 9,792,540 9,902,468 9,756,870
Proved undeveloped reserves:      
Proved undeveloped reserves | MMcfe [1] 7,410,574 8,289,115 8,315,536
Beginning Balance | MMcfe [1] 18,191,583 18,072,406 15,262,361
Revisions | MMcfe [1] (608,211) 303,068 731,735
Extensions, discoveries and additions | MMcfe [1] 1,264,282 1,161,274 3,143,898
Property sales | MMcfe [1] (828,084) (511,811) (262,180)
Production | MMcfe [1] (816,456) (833,354) (803,408)
Ending Balance | MMcfe [1] 17,203,114 18,191,583 18,072,406
[1] Oil and NGLs volumes are converted to mcfe at the rate of one barrel equals six mcf based upon the approximate relative energy content of oil to natural gas, which is not indicative of the relationship between oil and natural gas prices.