Investment in Oil and Gas Properties - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Oil and Gas In Process Activities [Line Items]
Write-down of oil and gas properties	$ 47,130		$ 47,130
Capital expenditures related to oil and gas property investments	570,658		570,658		724,339
Oil [Member]
Oil and Gas In Process Activities [Line Items]
Average price of oil and gas properties			94.94
Natural Gas [Member]
Oil and Gas In Process Activities [Line Items]
Average price of oil and gas properties			4.19
Natural Gas Liquids [Member]
Oil and Gas In Process Activities [Line Items]
Average price of oil and gas properties			41.33
Canada [Member]
Oil and Gas In Process Activities [Line Items]
Capital expenditures related to oil and gas property investments	$ 25,700		$ 25,700		$ 10,600