Derivative Instruments (Outstanding Forward and Future Contracts) (Details) (Total derivatives not designated as hedging instruments, Future, USD $)	Dec. 31, 2014 oz
Silver (ounces)
Derivative [Line Items]
Amount	675,000
Notional Value	$ 10,500,000
Gold (ounces)
Derivative [Line Items]
Amount	200
Notional Value	200,000
Copper (pounds)
Derivative [Line Items]
Amount	300,000
Notional Value	800,000
Tin (metric tons)
Derivative [Line Items]
Amount	35
Notional Value	$ 700,000