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 of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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- Definition

Amount, net of accumulated depreciation, depletion and amortization, of long-lived physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Property, Plant And Equipment (Property, Plant And Equipment By Major Classification) (Details) (USD $)															6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Land And Land Improvements [Member]	Dec. 31, 2012 Land And Land Improvements [Member]	Jun. 30, 2013 Mining And Other Equipment And Related Facilities [Member]	Dec. 31, 2012 Mining And Other Equipment And Related Facilities [Member]	Jun. 30, 2013 Mine Development Costs [Member]	Dec. 31, 2012 Mine Development Costs [Member]	Jun. 30, 2013 Coal Properties And Oil And Natural Gas Properties [Member]	Dec. 31, 2012 Coal Properties And Oil And Natural Gas Properties [Member]	Jun. 30, 2013 Construction Work In Process [Member]	Dec. 31, 2012 Construction Work In Process [Member]	Jun. 30, 2013 Oil And Natural Gas Properties [Member]	Dec. 31, 2012 Oil And Natural Gas Properties [Member]	Jun. 30, 2013 Minimum [Member] Mining And Other Equipment And Related Facilities [Member]	Jun. 30, 2013 Minimum [Member] Mine Development Costs [Member]	Jun. 30, 2013 Minimum [Member] Coal Properties And Oil And Natural Gas Properties [Member]	Jun. 30, 2013 Maximum [Member] Mining And Other Equipment And Related Facilities [Member]	Jun. 30, 2013 Maximum [Member] Mine Development Costs [Member]	Jun. 30, 2013 Maximum [Member] Coal Properties And Oil And Natural Gas Properties [Member]
Property, Plant and Equipment [Line Items]
Useful Lives															2 years	1 year	1 year	20 years	15 years	15 years
Total	$ 694,027,000	$ 683,669,000	$ 34,978,000	$ 34,978,000	$ 299,342,000	$ 297,615,000	$ 68,534,000	$ 67,045,000	$ 280,375,000	$ 278,088,000	$ 10,798,000	$ 5,943,000	$ 42,674	$ 37,720
Less accumulated depreciation, depletion and amortization	(234,990,000)	(219,709,000)
Net	$ 459,037,000	$ 463,960,000