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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, 2019
MMcfe
MMcf
MBbls
Dec. 31, 2018
MMcfe
MMcf
MBbls
Dec. 31, 2017
MMcfe
MMcf
MBbls
Proved undeveloped reserves:      
Proved undeveloped reserves | MMcfe 8,289,115 8,315,536  
Natural Gas      
Reserve Quantities [Line Items]      
Beginning Balance | MMcf 12,027,702 10,263,649 7,870,416
Revisions | MMcf 33,122 178,595 70,222
Extensions, discoveries and additions | MMcf 959,901 2,269,427 2,866,103
Purchases | MMcf   0 7,738
Property sales | MMcf (327,634) (135,884) (60,278)
Production | MMcf (578,114) (548,085) (490,552)
Ending Balance | MMcf 12,114,977 12,027,702 10,263,649
Proved developed reserves:      
Proved developed reserves | MMcf 6,486,211 6,451,012 5,437,674
Proved undeveloped reserves:      
Proved undeveloped reserves | MMcf 5,628,766 5,576,690 4,825,975
NGLs      
Reserve Quantities [Line Items]      
Beginning Balance 921,594 763,264 630,066
Revisions 57,311 84,993 83,338
Extensions, discoveries and additions 26,505 128,436 87,572
Purchases   0 330
Property sales (28,324) (16,774) (2,356)
Production (38,850) (38,325) (35,686)
Ending Balance 938,236 921,594 763,264
Proved developed reserves:      
Proved developed reserves 535,007 512,318 448,258
Proved undeveloped reserves:      
Proved undeveloped reserves 403,229 409,276 315,006
Crude Oil and Condensate      
Reserve Quantities [Line Items]      
Beginning Balance 85,856 69,854 70,252
Revisions (12,320) 7,197 (10,555)
Extensions, discoveries and additions 7,057 17,309 15,997
Purchases   0 66
Property sales (2,371) (4,276) (1,121)
Production (3,690) (4,228) (4,785)
Ending Balance 74,532 85,856 69,854
Proved developed reserves:      
Proved developed reserves 34,369 38,658 36,808
Proved undeveloped reserves:      
Proved undeveloped reserves 40,163 47,198 33,046
Natural Gas Equivalents      
Proved developed reserves:      
Proved developed reserves | MMcfe [1] 9,902,468 9,756,870 8,348,074
Proved undeveloped reserves:      
Proved undeveloped reserves | MMcfe [1] 8,289,115 8,315,536 6,914,287
Beginning Balance | MMcfe [1] 18,072,406 15,262,361 12,072,322
Revisions | MMcfe [1] 303,068 731,735 506,919
Extensions, discoveries and additions | MMcfe [1] 1,161,274 3,143,898 3,487,519
Purchases | MMcfe [1]   0 10,116
Property sales | MMcfe [1] (511,811) (262,180) (81,133)
Production | MMcfe [1] (833,354) (803,408) (733,382)
Ending Balance | MMcfe [1] 18,191,583 18,072,406 15,262,361
[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.