Annual report pursuant to Section 13 and 15(d)

Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Costs Incurred In Oil and Gas Property Acquisition and Development Activities (Details)

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Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) - Costs Incurred In Oil and Gas Property Acquisition and Development Activities (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]      
Acquisition $ 152,887 $ 810,755 $ 440,288
Development of proved undeveloped properties 423,998 642,811 864,511
Exploratory 0 0 2,249
Recompletions 16,386 13,894 45,658
Capitalized asset retirement obligation 10,971 8,800 2,095
Total 604,242 1,476,260 1,354,801
Investment in Grizzly Oil Sands ULC      
Costs Incurred, Oil and Gas Property Acquisition, Exploration, and Development Activities [Line Items]      
Acquisition 357 396 1,230
Development of proved undeveloped properties 0 47 7,107
Exploratory 0 0 0
Capitalized asset retirement obligation 784 282 1,055
Total $ 1,141 $ 725 $ 9,392