Acquisitions and Divestitures (Details) - km²	1 Months Ended			3 Months Ended
	Apr. 30, 2016	Feb. 29, 2016	Jan. 31, 2016	Mar. 31, 2016
Farm-in agreement | Block 5
Acquisitions and Divestitures
Participation interest acquired (as a percent)			65.00%
Farm-in agreement | Block 12
Acquisitions and Divestitures
Participation interest acquired (as a percent)		65.00%
Chevron | Farm-out agreements | Block 42
Acquisitions and Divestitures
Non operated interest	0.3333%
Hess Corporation | Farm-out agreements | Block 42
Acquisitions and Divestitures
Non operated interest	0.3333%
3 D seismic requirements (in square kilometers)	6,500
Agencia Nacional Do Petroleo De Sao Tome E Principe | Farm-in agreement | Block 5
Acquisitions and Divestitures
Carried interest held by National Petroleum Agency			15.00%
Agencia Nacional Do Petroleo De Sao Tome E Principe | Farm-in agreement | Block 12
Acquisitions and Divestitures
Carried interest held by National Petroleum Agency				12.50%