Investment in Oil and Gas Properties - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) $ / bbl $ / Mcf $ / Bngl	Mar. 31, 2015 USD ($) $ / bbl $ / Mcf $ / Bngl	Jun. 30, 2015 USD ($) $ / bbl $ / Mcf $ / Bngl
Oil and Gas In Process Activities [Line Items]
Write-down of oil and gas properties	$ 224,294		$ 715,706
Average 12-month oil prices net of differentials | $ / bbl	68.68	78.99	68.68
Average 12-month gas prices net of differentials | $ / Mcf	2.47	2.96	2.47
Decrease in written down value of oil and gas properties		$ 28,700	$ 47,800
Canada [Member]
Oil and Gas In Process Activities [Line Items]
Write-down of oil and gas properties			45,200
Oil And Gas [Member]
Oil and Gas In Process Activities [Line Items]
Write-down of oil and gas properties		$ 491,400	$ 179,100
Natural Gas Liquids (MBbls) [Member]
Oil and Gas In Process Activities [Line Items]
Average 12-month gas prices net of differentials | $ / Bngl	29.13	28.82	29.13