Debt (Details) (USD $)	3 Months Ended		6 Months Ended									3 Months Ended	6 Months Ended					1 Months Ended		6 Months Ended	0 Months Ended	3 Months Ended	6 Months Ended	0 Months Ended	3 Months Ended	6 Months Ended	0 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Senior Secured Notes	Dec. 31, 2012 Senior Secured Notes	Jun. 30, 2013 Senior Unsecured Notes	Dec. 31, 2012 Senior Unsecured Notes	Jun. 30, 2013 tMEDS	Dec. 31, 2012 tMEDS	Jun. 30, 2013 Equipment Loans	Jun. 30, 2013 Equipment Loans	Jun. 30, 2012 Equipment Loans	Dec. 31, 2012 Equipment Loans	Jun. 30, 2013 Other	Dec. 31, 2012 Other	Dec. 31, 2011 Mobile mining equipment loans unit	Jun. 30, 2013 Fixed Rate Loan	Jun. 30, 2013 Additional Fixed Rate Loan	Nov. 27, 2012 9.75% Senior Secured Notes Senior Secured Notes	Jun. 30, 2013 9.75% Senior Secured Notes Senior Secured Notes	Jun. 30, 2013 9.75% Senior Secured Notes Senior Secured Notes	May 11, 2012 12.5% Senior Unsecured Notes Senior Unsecured Notes	Jun. 30, 2013 12.5% Senior Unsecured Notes Senior Unsecured Notes	Jun. 30, 2013 12.5% Senior Unsecured Notes Senior Unsecured Notes	May 20, 2011 7.375% Senior Unsecured Notes Senior Unsecured Notes	Jun. 30, 2013 7.375% Senior Unsecured Notes Senior Unsecured Notes	Jun. 30, 2013 7.375% Senior Unsecured Notes Senior Unsecured Notes
Debt Instrument
Debt	$ 930,400,000		$ 930,400,000		$ 938,400,000	$ 347,000,000	$ 346,800,000	$ 550,000,000	$ 550,000,000	$ 25,200,000	$ 30,600,000	$ 8,000,000	$ 8,000,000		$ 10,600,000	$ 200,000	$ 400,000
Less: Current portion	(16,000,000)		(16,000,000)		(16,600,000)
Long-term debt	914,400,000		914,400,000		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	0	8,200,000	0	8,200,000																	10,000,000			6,900,000			10,100,000
Amortization of finance fees	0	500,000	0	1,200,000																	3,200,000
Cash interest paid	27,500,000	13,200,000	35,400,000	13,400,000								1,200,000	2,100,000	200,000									6,100,000		12,500,000			12,900,000
Interest costs capitalized												1,500,000	2,800,000	300,000								9,200,000	18,300,000		6,500,000	13,000,000		6,800,000	13,600,000
Debt fair market value																						361,900,000	361,900,000		191,500,000	191,500,000		288,100,000	288,100,000
Number of units of mobile mining equipment purchased (units)																		6
Outstanding payable amount																			$ 6,700,000	$ 1,300,000
Additional stated interest rate (percent)																				5.90%