Commitments and Contingencies (Details) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended			3 Months Ended					3 Months Ended		0 Months Ended	3 Months Ended
	Mar. 31, 2013 USD ($)	Mar. 31, 2012 USD ($)	Dec. 31, 2012 agreements	Mar. 31, 2013 CAD	Mar. 31, 2013 Molybdenum purchases pound	Mar. 31, 2013 Mt. Milligan	Mar. 31, 2013 Mt. Milligan Engineering and Equipment USD ($)	Mar. 31, 2013 Mt. Milligan Permanent Operations USD ($)	Dec. 31, 2014 Fixed Priced Contracts Molybdenum sales USDPerGBP	Mar. 31, 2013 Fixed Priced Contracts Molybdenum sales USDPerGBP pound	Mar. 31, 2013 Two Copper Concentrate Sales Contracts t	Mar. 31, 2013 One Copper Concentrate Sales Contract t	May 20, 2011 7.375% Senior Unsecured Notes Senior Unsecured Notes USD ($)	Mar. 31, 2013 7.375% Senior Unsecured Notes Senior Unsecured Notes USD ($)	Mar. 31, 2012 7.375% Senior Unsecured Notes Senior Unsecured Notes USD ($)
Commitments and Contingencies
Stated Interest rate (percent)													7.375%
Purchase commitment from 2013 to 2016 (in pounds)					9,600,000
Sale commitment during 2012 (in pounds)										64,000
Sale commitment average price (in dollars per pound)									12.93	12.93
Copper concentrate sales agreements			3
Agreement to sell copper-gold-silver (percent)						85.00%
Number of dry metric tons agreed to sell, per year during each of 2015 and 2016 (dry metric tons)											120,000	40,000
Open Purchase orders, contracts and capital purchase commitments							$ 100.6	$ 6.5
Maximum guarantee amount				16.5
Guarantee amount				5.3
Surety bond				11.2
Reimburse amount (percent)				25.00%
Proceeds received from issuance of debt													339.9
Financing fees for issuance of debt													10.1
Cash interest paid	7.9	0.2												6.8	7.0
Debt fair market value														$ 284.2