Depreciation, Depletion, Accretion and Amortization Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Depreciation, Depletion, Accretion and Amortization
Depreciation	$ 301,146		$ 328,072		$ 349,460
Depletion	10,607		11,195		10,337
Accretion	7,956		8,195		8,641
Amortization of leaseholds	381		225		195
Amortization of intangibles	11,869		14,032		13,460
Total	$ 331,959	[1]	$ 361,719	[1]	$ 382,093	[1]

[1] The allocation of indirect depreciation to our operating segments was changed in 2012 to better align the presentation with how management views information internally. The 2011 and 2010 DDA&A amounts presented above have been revised to conform to the 2012 presentation.