Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended											3 Months Ended		9 Months Ended					0 Months Ended		9 Months Ended	0 Months Ended	3 Months Ended	9 Months Ended	0 Months Ended	3 Months Ended	9 Months Ended	0 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012	Sep. 30, 2013 Senior Secured Notes	Dec. 31, 2012 Senior Secured Notes	Sep. 30, 2013 Senior Unsecured Notes	Dec. 31, 2012 Senior Unsecured Notes	Sep. 30, 2013 tMEDS	Dec. 31, 2012 tMEDS	Sep. 30, 2013 Equipment Loans	Sep. 30, 2012 Equipment Loans	Sep. 30, 2013 Equipment Loans	Sep. 30, 2012 Equipment Loans	Dec. 31, 2012 Equipment Loans	Sep. 30, 2013 Other	Dec. 31, 2012 Other	Dec. 08, 2010 Mobile mining equipment loans unit	Sep. 30, 2013 Fixed Rate Loan	Sep. 30, 2013 Additional Fixed Rate Loan	Nov. 27, 2012 9.75% Senior Secured Notes Senior Secured Notes	Sep. 30, 2013 9.75% Senior Secured Notes Senior Secured Notes	Sep. 30, 2013 9.75% Senior Secured Notes Senior Secured Notes	May 11, 2012 12.5% Senior Unsecured Notes Senior Unsecured Notes	Sep. 30, 2013 12.5% Senior Unsecured Notes Senior Unsecured Notes	Sep. 30, 2013 12.5% Senior Unsecured Notes Senior Unsecured Notes	May 20, 2011 7.375% Senior Unsecured Notes Senior Unsecured Notes	Sep. 30, 2013 7.375% Senior Unsecured Notes Senior Unsecured Notes	Sep. 30, 2013 7.375% Senior Unsecured Notes Senior Unsecured Notes
Debt Instrument
Debt	$ 926.0				$ 926.0				$ 938.4	$ 347.2	$ 346.8	$ 550.0	$ 550.0	$ 22.3	$ 30.6	$ 6.3		$ 6.3		$ 10.6	$ 0.2	$ 0.4
Less: Current portion	(15.3)				(15.3)				(16.6)
Long-term debt	910.7				910.7				921.8
Principal amount																							12.8			350.0			200.0			350.0
Stated Interest rate (percent)																5.50%		5.50%						3.60%		9.75%			12.50%			7.375%
Proceeds received from issuance of debt																										336.8			193.1			339.9
Financing fees for issuance of debt	0		3.0		0		11.2																			10.0			6.9			10.1
Amortization of finance fees	0		0.9		0		2.1																			3.2
Cash interest paid	19.1	[1]	1.4	[1]	54.5	[1]	14.8	[1]								1.4	0.1	3.5	0.4								17.0	23.1		12.5			12.9
Interest costs capitalized																0.9	0.5	3.7	0.8								9.2	27.5		6.5	19.5		6.8	20.4
Debt fair market value																											386.4	386.4		206.5	206.5		306.7	306.7
Number of units of mobile mining equipment purchased (units)																							6
Outstanding payable amount																								$ 6.0	$ 0.3
Additional stated interest rate (percent)																									5.90%

[1] For the three and nine months ended September 30, 2013, the cash interest paid of $19.1 million and $54.5 million, respectively, had been previously capitalized related to the Company's debt, as described in Note 9. For the three and nine months ended September 30, 2012, the cash interest paid of $1.4 million and $14.8 million, respectively, had been previously capitalized related to the Company's debt, as described in Note 9.