Impairment of Proved Properties - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Impairment Of Proved Properties [Line Items]
Company recognized an impairment loss	$ 98.3		$ 7.6
Impairment of Oil and Gas Properties		0
Etame field
Impairment Of Proved Properties [Line Items]
Company recognized an impairment loss	38.5
Ebouri field
Impairment Of Proved Properties [Line Items]
Company recognized an impairment loss	5.9
Southeast Etame And North Tchibala field
Impairment Of Proved Properties [Line Items]
Company recognized an impairment loss	$ 53.9