DERIVATIVE INSTRUMENTS: (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012 Zero cost collar contracts lb	Dec. 31, 2011 Zero cost collar contracts lb	Dec. 31, 2011 Swap contracts lb
DERIVATIVE INSTRUMENTS:
Minimum correlation coefficient between average monthly copper prices on LME and COMEX exchanges (as a percent)		99.90%
Copper derivative activity related to copper sales transactions
Pounds			46,300,000	423,300,000	390,800,000
Average LME cap price (in dollars per unit)			5.18	3.63
Average LME floor price (in dollars per unit)			3.50	2.27
Weighted average COMEX price					3.46
Realized gain (loss) on copper derivatives	$ 13.5				$ 13.5