Acquisitions and Divestitures (Details) $ in Thousands, $ / site in Millions		1 Months Ended					3 Months Ended		12 Months Ended
	Dec. 31, 2015	Jan. 31, 2016	Nov. 30, 2015	Oct. 31, 2015	Mar. 31, 2015 USD ($) item	Aug. 31, 2014 $ / site	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($) agreement item $ / site	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Acquisitions and Divestitures
Gain on sale of assets									$ 24,651	$ 23,769
Farm-in agreement | Camarao, Ameijoa, Mexilhao and Ostra blocks
Acquisitions and Divestitures
Participating interests (as a percent)					31.00%
Farm-in agreement | Block 11
Acquisitions and Divestitures
Participation interest acquired (as a percent)				85.00%
Farm-in agreement | Block 5
Acquisitions and Divestitures
Participation interest acquired (as a percent)		65.00%
Farm-in agreement | Block 6
Acquisitions and Divestitures
Participation interest acquired (as a percent)			45.00%
Farm-out agreements | Block C8
Acquisitions and Divestitures
Participating interests (as a percent)	90.00%
Farm-out agreements | Block C12
Acquisitions and Divestitures
Participating interests (as a percent)	90.00%
Farm-out agreements | Block C13
Acquisitions and Divestitures
Participating interests (as a percent)	90.00%
Farm-out agreements | Essaouira Offshore Block
Acquisitions and Divestitures
Participating interests (as a percent)									30.00%
Farm-out agreements | Foum Assaka Offshore Block
Acquisitions and Divestitures
Participating interests (as a percent)									29.90%
Farm-out agreements | Tarhazoute Offshore Block
Acquisitions and Divestitures
Participating interests (as a percent)									30.00%
Farm-out agreements | Cap Boujdour Offshore block
Acquisitions and Divestitures
Participating interests (as a percent)									55.00%
Timis Corporation Limited | Farm-in agreement | Cayar Offshore Profond And Saint Louis Offshore Profond Blocks
Acquisitions and Divestitures
Participation interest acquired (as a percent)						60.00%
Maximum cost per contingent exploration well | $ / site						120.0
Participating interest for carrying the full cost of third contingent exploration or appraisal well (as a percent)						65.00%
Chevron | Farm-out agreements | Block C8, Block 12 and Block 13
Acquisitions and Divestitures
Participation interest acquired (as a percent)					30.00%
Number of exploration wells for which a third party will pay a disproportionate amount | item					1
Proceeds on sale of assets					$ 28,700
Gain on sale of assets					$ 24,700
Agencia Nacional Do Petroleo De Sao Tome E Principe | Farm-in agreement | Block 11
Acquisitions and Divestitures
Carried interest held by National Petroleum Agency				15.00%
BP | Farm-out agreements | Essaouira Offshore, Foum Assaka Offshore and Tarhazoute Offshore blocks
Acquisitions and Divestitures
Number of farm-out agreements | agreement								3
Number of blocks covered by farm-out agreements | item								3
Proceeds on sale of assets								$ 56,900
Gain on sale of assets										$ 23,800
Number of exploration wells in each block for which our share of costs will be paid for by a third party | item								1
Percentage of third party's share of drilling costs to be paid in the event of drilling a second exploration well in each block								150.00%
BP | Farm-out agreements | Essaouira Offshore, Foum Assaka Offshore and Tarhazoute Offshore blocks | Maximum
Acquisitions and Divestitures
Spending per well by third party for first exploration well (in dollars per well) | $ / site								120.0
Spending per well by third party in the event of drilling a second exploration well (in dollars per well) | $ / site								120.0
Cairn | Farm-out agreements | Cap Boujdour Offshore block
Acquisitions and Divestitures
Reimbursement of shared costs previously incurred							$ 1,500
Participation interest acquired (as a percent)								20.00%
Percentage of third party's share of seismic and drilling costs								150.00%
Amount of our future costs paid for by third party								$ 12,300
Cairn | Farm-out agreements | Cap Boujdour Offshore block | Maximum
Acquisitions and Divestitures
Spending by third party for seismic costs								25,000
Spending by third party for an exploration well								$ 100,000