Gabon - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Feb. 28, 2013	Dec. 31, 2013 Sqkms ft	Dec. 31, 2013 Dussafu PSC [Member] sqmi acre ft	Dec. 31, 2012 Dussafu PSC [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Ownership percentage held by wholly owned subsidiary	75.00%		66.667%
Area covered by acquiree entity			680,000
Area covered by acquiree entity under water depths			1,650
Extended period of third exploration phase		4 years
Third exploration phase extension date		May 27, 2016
Processing of seismic		545
Depth of well		11,385
Acquisition of land as part of seismic acquisition survey			1,260
Oil and gas properties			$ 103.4	$ 76.4