Property, Plant and Equipment (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Land, surface rights, and mineral rights	Dec. 31, 2011 Land, surface rights, and mineral rights	Dec. 31, 2012 Mining equipment	Dec. 31, 2011 Mining equipment	Dec. 31, 2012 Construction in progress	Dec. 31, 2011 Construction in progress	Dec. 31, 2012 Other equipment	Dec. 31, 2011 Other equipment	Dec. 31, 2012 Buildings and improvements	Dec. 31, 2011 Buildings and improvements	Dec. 31, 2012 Mineral rights	Dec. 31, 2011 Mineral rights	Jun. 30, 2011 Mineral rights
Property, Plant and Equipment
Total	$ 2,697,698,000	$ 2,281,495,000		$ 1,699,148,000	$ 1,315,991,000	$ 843,262,000	$ 814,177,000	$ 18,277,000	$ 18,616,000	$ 65,588,000	$ 61,465,000	$ 71,422,000	$ 71,246,000
Less: accumulated depreciation and depletion	(1,019,404,000)	(931,360,000)
Property, plant and equipment, net	1,678,294,000	1,350,135,000														293,900,000
Gross amount of property, plant and equipment attributable to areas where the Company is not engaged in mining operations														963,100,000	743,200,000
Interest costs capitalized on mine development and construction projects
Interest costs capitalized	$ 41,975,000	$ 44,883,000	$ 24,487,000