Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2014

Property Plant And Equipment [Abstract]

Property and equipment consisted of the following at December 31, 2014 and 2013 (in thousands):

	2014			2013
Equipment	$	6,679,894		$	5,749,975
Oil and natural gas properties		196,234			183,571
Buildings		83,465			80,050
Land		12,038			12,054
		6,971,631			6,025,650
Less accumulated depreciation, depletion and impairment		(2,840,560	)		(2,390,109	)
Property and equipment, net	$	4,131,071		$	3,635,541

Summary of Depreciation, Depletion, Amortization and Impairment Expense related to Property and Equipment and Intangible Assets

Depreciation, depletion, amortization and impairment — The following table summarizes depreciation, depletion, amortization and impairment expense related to property and equipment and intangible assets for 2014, 2013 and 2012 (in thousands):

	2014		2013		2012
Depreciation and impairment expense	$	693,390	$	573,106	$	502,953
Amortization expense		3,643		3,993		4,110
Depletion expense		21,697		20,370		19,551
Total	$	718,730	$	597,469	$	526,614