Property, Plant & Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Property, Plant & Equipment
Total, gross	$ 6,705,546	$ 6,692,814
Less allowances for depreciation, depletion and amortization	3,287,367	3,059,900
Total, net	3,418,179	3,632,914
Land and land improvements [Member]
Property, Plant & Equipment
Total, gross	2,122,350	2,096,046
Buildings [Member]
Property, Plant & Equipment
Total, gross	163,178	159,458
Leaseholds [Member]
Property, Plant & Equipment
Total, gross	9,238	7,458
Machinery and equipment [Member]
Property, Plant & Equipment
Total, gross	4,206,870	4,222,242
Deferred asset retirement costs [Member]
Property, Plant & Equipment
Total, gross	136,289	142,441
Construction in progress [Member]
Property, Plant & Equipment
Total, gross	$ 67,621	$ 65,169

The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.

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Gross amount, at the balance sheet date, of long-lived physical assets used in the normal conduct of business and not intended for resale. This can include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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- Definition

Tangible assets that are held by an entity for use in the production or supply of goods and services, for rental to others, or for administrative purposes and that are expected to provide economic benefit for more than one year; net of accumulated depreciation. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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