Debt (Details) (USD $)	3 Months Ended													1 Months Ended		3 Months Ended	0 Months Ended	3 Months Ended	0 Months Ended	3 Months Ended	0 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Senior Secured Notes	Dec. 31, 2012 Senior Secured Notes	Mar. 31, 2013 Senior Unsecured Notes	Dec. 31, 2012 Senior Unsecured Notes	Mar. 31, 2013 tMEDS	Dec. 31, 2012 tMEDS	Mar. 31, 2013 Equipment Loans	Dec. 31, 2012 Equipment Loans	Mar. 31, 2013 Other	Dec. 31, 2012 Other	Dec. 31, 2011 Mobile mining equipment loans unit	Mar. 31, 2013 Fixed Rate Loan	Mar. 31, 2013 Additional Fixed Rate Loan	Nov. 27, 2012 9.75% Senior Secured Notes Senior Secured Notes	Mar. 31, 2013 9.75% Senior Secured Notes Senior Secured Notes	May 11, 2012 12.5% Senior Unsecured Notes Senior Unsecured Notes	Mar. 31, 2013 12.5% Senior Unsecured Notes Senior Unsecured Notes	May 20, 2011 7.375% Senior Unsecured Notes Senior Unsecured Notes	Mar. 31, 2013 7.375% Senior Unsecured Notes Senior Unsecured Notes	Mar. 31, 2012 7.375% Senior Unsecured Notes Senior Unsecured Notes
Debt Instrument
Debt	$ 934,500,000		$ 938,400,000	$ 346,900,000	$ 346,800,000	$ 550,000,000	$ 550,000,000	$ 27,900,000	$ 30,600,000	$ 9,500,000	$ 10,600,000	$ 200,000	$ 400,000
Less: Current portion	(16,400,000)		(16,600,000)
Long-term debt	918,100,000		921,800,000
Principal amount														12,800,000.0			350,000,000.0		200,000,000		350,000,000.0
Stated Interest rate (percent)															3.60%		9.75%		12.50%		7.375%
Proceeds received from issuance of debt																	336,800,000		193,100,000		339,900,000
Financing fees for issuance of debt																	10,000,000		6,900,000		10,100,000
Amortization of finance fees	0	700,000															3,200,000
Cash interest paid	7,900,000	200,000																6,100,000				6,800,000	7,000,000
Interest costs capitalized	1,300,000	200,000																9,100,000		6,500,000
Debt fair market value																		384,800,000		195,100,000		284,200,000
Number of units of mobile mining equipment purchased (units)														6
Outstanding payable amount															$ 7,300,000	$ 2,100,000
Additional stated interest rate (percent)																5.90%