Net Property and Equipment - Schedule of Net Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment, Net [Abstract]
Proved crude oil and natural gas properties	$ 12,423,878	$ 8,980,505
Unproved crude oil and natural gas properties	1,181,268	1,073,944
Service properties, equipment and other	236,233	170,763
Total property and equipment	13,841,379	10,225,212
Accumulated depreciation, depletion and amortization	(3,120,107)	(2,119,943)
Net property and equipment	$ 10,721,272	$ 8,105,269