China - Additional Information (Detail) (WAB-21 [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Extension of the license (Date)	May 31, 2015
Impaired carrying value		$ 2.9
License extended expiry date	May 31, 2013
China National Offshore Oil Corporation [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Petroleum contract coverage area	6,200,000
Additional coverage area	1,250,000