SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES: (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 segment Y	Dec. 31, 2011	Dec. 31, 2010
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES:
Average estimated recovery period of long-term leach stockpiles (in years)	5
Estimated useful lives of buildings and equipment, low end of range (in years)	5
Estimated useful lives of buildings and equipment, high end of range (in years)	40
Increase in total reserves at a property to qualify as a major expansion (as a percent)	10.00%
Period considered for calculation of average metal price (in years)	3
Current price of copper (in dollars per pound)	3.68	3.26	2.97
Average price of copper (in dollars per pound)	3.00
Average price of molybdenum (in dollars per pound)	12.00
Number of years of average prices for copper and molybdenum used for impairment analysis	3
Number of reportable segments	3
Financial information related to segments
Total property, net	$ 5,156,731	$ 4,429,906	$ 4,095,000
Maximum
Financial information related to segments
Maximum period after shipping within which pricing is based by customer contracts in most cases (in months)	3
Maximum maturity period of cash equivalents (in months)	3
Mine development
Financial information related to segments
Total property, net	37,900	39,800
Mexican IMMSA Unit
Financial information related to segments
Number of underground poly metal mines	5
Total property, net	350,900	320,100	296,300
Peruvian Operations
Financial information related to segments
Number of open-pit copper mines	2
Total property, net	$ 2,231,400	$ 2,225,900	$ 2,164,700