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Property and Equipment (Detail) (USD $)
In Thousands, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Property, Plant and Equipment [Line Items]    
Equipment $ 5,719,687 $ 5,387,490
Oil and natural gas properties 178,139 156,834
Buildings 80,113 66,490
Land 11,898 10,413
Property, Plant and Equipment, Gross, Total 5,989,837 5,621,227
Less accumulated depreciation and depletion (2,338,263) (2,005,844)
Property and equipment, net $ 3,651,574 $ 3,615,383