Investment in Oil and Gas Properties - Additional Information (Detail) (China, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Project	Dec. 31, 2011	Dec. 31, 2010
China
Oil and Gas In Process Activities [Line Items]
Interest costs capitalized on unevaluated properties	$ 37,656	$ 42,033	$ 30,783
Specifically identified drilling projects	124
Projects expected to be evaluated	4 years