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DERIVATIVE INSTRUMENTS: (Details) (Zero cost collar contracts, 2011, USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
lb
Zero cost collar contracts | 2011
 
Copper derivative activity related to copper sales transactions  
Pounds 46,300,000
Average cap price (in dollars per unit) 5.18
Average floor price (in dollars per unit) 3.50
Realized gain (loss) on copper derivatives $ 0