Commitments and Contingencies (Details) In Millions, unless otherwise specified	12 Months Ended			9 Months Ended					9 Months Ended		1 Months Ended
	Dec. 31, 2012 agreements	Sep. 30, 2013 CAD	Sep. 30, 2013 Molybdenum purchases pound	Sep. 30, 2013 Mt. Milligan	Sep. 30, 2013 Mt. Milligan Engineering and Equipment USD ($)	Sep. 30, 2013 Mt. Milligan Permanent Operations USD ($)	Dec. 31, 2013 Fixed Priced Contracts Molybdenum sales USDPerGBP	Sep. 30, 2013 Fixed Priced Contracts Molybdenum sales pound USDPerGBP	Sep. 30, 2013 Two Copper Concentrate Sales Contracts t	Sep. 30, 2013 One Copper Concentrate Sales Contract t	Oct. 31, 2012 Performance Guarantee TC Mine Phase 7	Sep. 30, 2013 ACE Group Guarantee Obligations Mt. Milligan and Endako Mine [Member] USD ($)	Sep. 30, 2013 ACE Group, Export Development Canada, and Royal Bank of Canada Guarantee Obligations Mt. Milligan and Endako Mine [Member]
Commitments and Contingencies
Purchase commitment from 2013 to 2016 (in pounds)			8,900,000
Sale commitment during 2012 (in pounds)								231,000
Sale commitment average price (in dollars per pound)							12.93	13.20
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					$ 9.7	$ 20.0
Maximum guarantee amount		16.5
Guarantee amount		5.3
Surety bond		11.2
Reimburse amount (percent)													1.70%
Payment for incentive fee period											60 days
Guarantor Obligation, Collateral Already Posted Under Guarantee												$ 7.0