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Supplementary Information - Reserve Quantity Information (Detail)
 12 Months Ended
Dec. 31, 2019
MBbls
MMcf
Dec. 31, 2018
MBbls
MMcf
Oil [Member]    
Proved Developed Reserves:    
Beginning of year 6,404 5,333
Extensions, discoveries and improved recovery 471 1,284
Revisions of previous estimates (1,260) 192
Converted from undeveloped reserves 7 605
Reserves sold (5) (3)
Reserve purchased 6 75
Production (1,242) (1,082)
End of year 4,381 6,404
Proved Undeveloped Reserves:    
Beginning of year 10 505
Extensions, discoveries and improved recovery 1,834 (123)
Revisions of previous estimates (4) 233
Converted to developed reserves (7) (605)
End of year 1,833 10
Total Proved Reserves at the End of the Year 6,214 6,414
NGLs [Member]    
Proved Developed Reserves:    
Beginning of year 2,707 1,703
Extensions, discoveries and improved recovery 264 438
Revisions of previous estimates 506 662
Converted from undeveloped reserves 7 258
Reserves sold 0 0
Reserve purchased 4 35
Production (574) (389)
End of year 2,914 2,707
Proved Undeveloped Reserves:    
Beginning of year 12 156
Extensions, discoveries and improved recovery 1,013 (22)
Revisions of previous estimates (1) 136
Converted to developed reserves (7) (258)
End of year 1,017 12
Total Proved Reserves at the End of the Year 3,931 2,719
Gas [Member]    
Proved Developed Reserves:    
Beginning of year | MMcf 21,065 17,143
Extensions, discoveries and improved recovery | MMcf 1,330 2,237
Revisions of previous estimates | MMcf 2,033 4,144
Converted from undeveloped reserves | MMcf 65 870
Reserves sold | MMcf (120) (368)
Reserve purchased | MMcf 19 179
Production | MMcf (4,397) (3,140)
End of year | MMcf 19,995 21,065
Proved Undeveloped Reserves:    
Beginning of year | MMcf 124 709
Extensions, discoveries and improved recovery | MMcf 4,530 (34)
Revisions of previous estimates | MMcf (42) 319
Converted to developed reserves | MMcf (65) (870)
End of year | MMcf 4,547 124
Total Proved Reserves at the End of the Year | MMcf 24,542 21,189