Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Equipment	$ 5,636,306	$ 5,387,490
Oil and natural gas properties	169,740	156,834
Buildings	67,683	66,490
Land	11,897	10,413
Property, Plant and Equipment, Gross, Total	5,885,626	5,621,227
Less accumulated depreciation and depletion	(2,219,873)	(2,005,844)
Property and equipment, net	$ 3,665,753	$ 3,615,383