Segment Reporting Revenue by Customer (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Mitsui [Member] | Palmarejo, Rochester [Member]
Revenue, Major Customer [Line Items]
Revenues	$ 133.8	$ 70.3	$ 65.6
TD Bank Group [Member] | Palmarejo, Rochester [Member]
Revenue, Major Customer [Line Items]
Revenues	106.7	106.7	65.8
Standard Bank [Member] | Palmarejo, Rochester [Member]
Revenue, Major Customer [Line Items]
Revenues	87.5	69.0	72.3
China Gold [Member] | Kensington [Member]
Revenue, Major Customer [Line Items]
Revenues	86.8	81.5	43.8
Johnson Matthey [Member] | San Bartolome [Member]
Revenue, Major Customer [Line Items]
Revenues	71.8	66.4	1.7
Valcambi [Member] | Palmarejo San Bartolome [Member]
Revenue, Major Customer [Line Items]
Revenues	33.9	77.2	414.4
International Commodities [Member] | Palmarejo San Bartolome Rochester [Member]
Revenue, Major Customer [Line Items]
Revenues	22.4	84.6	58.0
Auramet [Member] | Palmarejo, San Bartolome, Kensington, Rochester [Member]
Revenue, Major Customer [Line Items]
Revenues	$ 10.8	$ 111.7	$ 94.6