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Investment in Oil and Gas Properties - Additional Information (Detail)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2016
USD ($)
$ / Mcf
$ / bbl
Mar. 31, 2016
USD ($)
$ / Mcf
$ / bbl
Jun. 30, 2016
USD ($)
$ / Mcf
$ / bbl
Jun. 30, 2015
USD ($)
Jun. 30, 2016
USD ($)
$ / Mcf
$ / bbl
Jun. 30, 2015
USD ($)
Dec. 31, 2015
$ / Mcf
$ / bbl
Oil and Gas In Process Activities [Line Items]              
Write-down of oil and gas properties     $ 118,649 $ 224,294 $ 247,853 $ 715,706  
Decrease in written down value of oil and gas properties   $ 23,000 $ 18,100        
Oil And Gas              
Oil and Gas In Process Activities [Line Items]              
Write-down of oil and gas properties $ 118,600 $ 128,900          
Oil              
Oil and Gas In Process Activities [Line Items]              
Average 12-month oil prices net of differentials | $ / bbl 43.49 46.72 43.49   43.49   51.16
Natural Gas              
Oil and Gas In Process Activities [Line Items]              
Average twelve month gas prices net of differentials | $ / Mcf 1.93 2.01 1.93   1.93   2.19
Natural Gas Liquids (MBbls)              
Oil and Gas In Process Activities [Line Items]              
Average 12-month gas prices net of differentials | $ / bbl 9.33 13.65 9.33   9.33   16.40
CANADA              
Oil and Gas In Process Activities [Line Items]              
Write-down of oil and gas properties   $ 300