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Depreciation, Depletion, Amortization and Impairment Expense Related to Property and Equipment and Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Depreciation and Other Amortization Expenses [Line Items]
Depreciation and impairment expense	$ 502,953	$ 419,183	$ 322,308
Amortization expense	4,110	4,110	1,027
Depletion expense	19,551	13,986	10,158
Total	$ 526,614	$ 437,279	$ 333,493

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

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