Investment in Oil and Gas Properties - Additional Information (Detail) $ in Thousands				3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) $ / Bngl $ / Mcf $ / bbl	Jun. 30, 2015 USD ($) $ / Bngl $ / Mcf $ / bbl	Mar. 31, 2015 USD ($) $ / Bngl $ / Mcf $ / bbl	Sep. 30, 2015 USD ($) $ / Bngl $ / Mcf $ / bbl	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) $ / Bngl $ / Mcf $ / bbl	Sep. 30, 2014 USD ($)
Oil and Gas In Process Activities [Line Items]
Write-down of oil and gas properties				$ 295,679	$ 47,130	$ 1,011,385	$ 47,130
Average 12-month oil prices net of differentials | $ / bbl	57.76	68.68	78.99	57.76		57.76
Average 12-month gas prices net of differentials | $ / Mcf	2.44	2.47	2.96	2.44		2.44
Decrease in written down value of oil and gas properties		$ 47,800	$ 28,700			$ 42,700
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	$ 295,700	$ 179,100	$ 491,400
Natural Gas Liquids (MBbls) [Member]
Oil and Gas In Process Activities [Line Items]
Average 12-month gas prices net of differentials | $ / Bngl	23.04	29.13	28.82	23.04		23.04