Property and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Equipment	$ 5,228,179	$ 4,730,925
Oil and natural gas properties	151,074	131,812
Buildings	62,894	64,090
Land	10,266	11,467
Property, Plant and Equipment, Gross, Total	5,452,413	4,938,294
Less accumulated depreciation and depletion	(1,929,509)	(1,771,028)
Property and equipment, net	$ 3,522,904	$ 3,167,266