Derivative Instruments (Outstanding Forward and Future Contracts) (Details) (Not Designated as Hedging Instrument, Futures and Forwards Contracts, USD $)	Dec. 31, 2013 oz
Silver, Ounces
Derivative [Line Items]
Outstanding forward and future contracts (in ounces)	650,000
Notional amount of debt	$ 12,600,000
Gold, Ounces
Derivative [Line Items]
Outstanding forward and future contracts (in ounces)	1,000
Notional amount of debt	1,200,000
Copper, Ounces
Derivative [Line Items]
Outstanding forward and future contracts (in ounces)	350,000
Notional amount of debt	1,200,000
Tin, Ounces
Derivative [Line Items]
Outstanding forward and future contracts (in ounces)	40
Notional amount of debt	$ 900,000