Net Costs Incurred on Unevaluated Properties (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Extractive Industries [Abstract]
Acquisition costs evaluated during the year	$ 30,271	$ 9,739	$ (2,397)
Exploration costs evaluated during the year	188,830	(1,209)	(51,207)
Capitalized interest costs evaluated during the year	46,860	37,656	42,033
Total costs incurred during the year, net of divestitures	$ 265,961	$ 46,186	$ (11,571)