Divestitures - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Jul. 31, 2014 GOM Conventional Shelf [Member]	Jan. 16, 2014 Cut Off and Clovelly Fields [Member]	Jan. 31, 2014 Hatch Point Field [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale of interest cash consideration	$ 223,299,000	$ 6,300,000			$ 44,800,000	$ 9,700,000
Estimates asset retirement obligations				125,100,000	9,200,000	1,200,000
Cash consideration received on sale of interest				$ 177,600,000
Percentage of estimated proved oil and natural gas reserves			9.00%