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Supplementary Information - Reserve Quantity Information (Detail)
 12 Months Ended
Dec. 31, 2016
MMcf
MBbls
Dec. 31, 2015
MMcf
MBbls
Oil [Member]    
Proved Developed Reserves:    
Beginning of year 4,579 6,239
Extensions, discoveries and improved recovery 577 47
Revisions of previous estimates (1,425) (1,650)
Converted from undeveloped reserves 46 677
Reserves sold   (53)
Reserves purchased   39
Production (670) (720)
End of year 3,107 4,579
Proved Undeveloped Reserves:    
Beginning of year 52 14,709
Extensions, discoveries and improved recovery 635 420
Revisions of previous estimates 2 (14,400)
Converted to developed reserves (46) (677)
End of year 643 52
Total Proved Reserves at the End of the Year 3,750 4,631
NGLs [Member]    
Proved Developed Reserves:    
Beginning of year 1,673 2,160
Extensions, discoveries and improved recovery 176 85
Revisions of previous estimates (527) (560)
Converted from undeveloped reserves 14 163
Reserves sold (1)  
Reserves purchased   12
Production (70) (187)
End of year 1,265 1,673
Proved Undeveloped Reserves:    
Beginning of year 12 4,322
Extensions, discoveries and improved recovery 157 101
Revisions of previous estimates 4 (4,248)
Converted to developed reserves (14) (163)
End of year 159 12
Total Proved Reserves at the End of the Year 1,424 1,685
Gas [Member]    
Proved Developed Reserves:    
Beginning of year | MMcf 23,275 32,267
Extensions, discoveries and improved recovery | MMcf 1,136 2,067
Revisions of previous estimates | MMcf (7,342) (8,368)
Converted from undeveloped reserves | MMcf 65 944
Reserves sold | MMcf (7) (26)
Reserves purchased | MMcf   372
Production | MMcf (4,126) (3,981)
End of year | MMcf 13,001 23,275
Proved Undeveloped Reserves:    
Beginning of year | MMcf 55 26,331
Extensions, discoveries and improved recovery | MMcf 1,994 701
Revisions of previous estimates | MMcf 19 (26,033)
Converted to developed reserves | MMcf (65) (944)
End of year | MMcf 2,003 55
Total Proved Reserves at the End of the Year | MMcf 15,004 23,330