Leases (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Equipment Facility Mt. Milligan Project	Dec. 31, 2012 Equipment Facility Mt. Milligan Project	Mar. 30, 2011 Equipment Facility Mt. Milligan Project	Mar. 30, 2011 Minimum Equipment Facility	Mar. 30, 2011 Maximum Equipment Facility
Capital Lease
Maximum underwriting available under facility					$ 132,000,000
Term of borrowing under facility (in months)						48 months	60 months
Interest costs capitalized	1,300,000	200,000
Interest related to equipment facility paid	900,000	0
Cash from sale of equipment	27,300,000
Capital lease obligations incurred	24,600,000
Capital lease obligations upfront payment	2,700,000
Capital leases			28,200,000	29,800,000
Sales-leaseback			64,900,000	42,300,000
Capital lease obligations			$ 93,100,000	$ 72,100,000