Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Oil and Gas Reserves (Details)

v3.8.0.1
Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Oil and Gas Reserves (Details)
bbl in Thousands, Mcf in Thousands
 12 Months Ended
Dec. 31, 2017
bbl
Mcf
Dec. 31, 2016
bbl
Mcf
Dec. 31, 2015
bbl
Mcf
Oil derivatives      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning of the period 5,546 6,458 9,497
Purchases in oil and natural gas reserves in place 15,132 0 0
Extensions and discoveries 951 1,217 2,413
Revisions of prior reserve estimates 107 (3) (2,553)
Current production (2,579) (2,126) (2,899)
End of period 19,157 5,546 6,458
Proved developed reserves 10,245 4,882 6,120
Proved undeveloped reserves 8,912 664 338
Natural gas liquids derivatives      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning of the period | Mcf 2,167,068 1,560,145 719,006
Purchases in oil and natural gas reserves in place | Mcf 1,098,644 0 371,663
Extensions and discoveries | Mcf 1,594,734 1,082,220 997,057
Revisions of prior reserve estimates | Mcf 314,925 (247,703) (371,430)
Current production | Mcf (350,061) (227,594) (156,151)
End of period | Mcf 4,825,310 2,167,068 1,560,145
Proved developed reserves | Mcf 1,616,930 744,797 652,961
Proved undeveloped reserves | Mcf 3,208,380 1,422,271 907,184
Natural gas liquids      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning of the period 20,127 17,736 26,268
Purchases in oil and natural gas reserves in place 53,617 0 0
Extensions and discoveries 4,619 7,677 5,486
Revisions of prior reserve estimates 2,737 (1,439) (9,594)
Current production (5,334) (3,847) (4,424)
End of period 75,766 20,127 17,736
Proved developed reserves 36,247 14,299 12,910
Proved undeveloped reserves 39,519 5,828 4,826
Investment in Grizzly Oil Sands ULC | Oil derivatives      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning of the period 0 0 14,558
Purchases in oil and natural gas reserves in place 0 0 0
Extensions and discoveries 0 0 0
Revisions of prior reserve estimates 0 0 (14,530)
Current production 0 0 (28)
End of period 0 0 0
Proved developed reserves 0 0 0
Proved undeveloped reserves 0 0 0
Investment in Grizzly Oil Sands ULC | Natural gas liquids derivatives      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning of the period | Mcf 0 0 0
Purchases in oil and natural gas reserves in place | Mcf 0 0 0
Extensions and discoveries | Mcf 0 0 0
Revisions of prior reserve estimates | Mcf 0 0 0
Current production | Mcf 0 0 0
End of period | Mcf 0 0 0
Proved developed reserves | Mcf 0 0 0
Proved undeveloped reserves | Mcf 0 0 0
Investment in Grizzly Oil Sands ULC | Natural gas liquids      
Proved Developed and Undeveloped Reserves [Roll Forward]      
Beginning of the period 0 0 0
Purchases in oil and natural gas reserves in place 0 0 0
Extensions and discoveries 0 0 0
Revisions of prior reserve estimates 0 0 0
Current production 0 0 0
End of period 0 0 0
Proved developed reserves 0 0 0
Proved undeveloped reserves 0 0 0