Financial Instruments (Unaudited) Not Designated as Hedging Instruments (Details) - Jun. 30, 2015 oz in Thousands, lb in Millions	lb oz $ / lb $ / oz
Embedded derivatives in provisional sales contracts - Copper [Member] | Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz) | lb	572
Average contract price	2.68
Average market price	2.58
Maturities through	Nov. 30, 2015
Embedded derivatives in provisional sales contracts - Gold [Member] | Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz) | oz	229
Average contract price | $ / oz	1,189
Average market price | $ / oz	1,174
Maturities through	Sep. 30, 2015
Embedded derivatives in provisional purchase contracts - Copper [Member] | Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz) | lb	134
Average contract price	2.75
Average market price	2.61
Maturities through	Oct. 31, 2015
Atlantic Copper [Member] | Copper forward contracts [Member] | Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz) | lb	31
Average contract price	2.65
Maturities through	Aug. 31, 2015
Copper futures and swap contracts [Member] | Fair Value Hedging [Member] | Derivatives designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz) | lb	51
Average contract price	2.71
Maturities through	May 31, 2017