COMMITMENTS AND CONTINGENCIES: (Details 3) PEN in Millions, $ in Millions	1 Months Ended		9 Months Ended											12 Months Ended
	Jul. 31, 2014 MW	Jun. 30, 2014 MW	Sep. 30, 2015	Sep. 30, 2015 MW	Sep. 30, 2015 m	Sep. 30, 2015 ft	Sep. 30, 2015 mi	Sep. 30, 2015 km	Sep. 30, 2015	Sep. 30, 2015 item	Sep. 30, 2015 T	Sep. 30, 2015 PEN	Sep. 30, 2015 USD ($)	Dec. 31, 2014 PEN	Dec. 31, 2014 USD ($)	Dec. 31, 2005 item	Dec. 31, 1997
Mexico
Other commitments:
Commitment for capital projects													$ 348.6
Tia Maria | Peru
Other commitments:
Project Budget													1,400.0
Annual production ( in tons) | T											120,000
Distance of sea water transportation							15.5	25
Additional investment in desalinization plant													95.0
Height above sea level of the desalinization plant					1,000	3,300
Term life of environmental project (in years)			20 years
Number of jobs expected to be generated | item										3,500
Number of workers expected to be directly employed | item										600
Number of workers expected to be indirectly employed | item										2,000
Amount expended in current year													360.2
Toquepala Concentrator Expansion | Peru
Other commitments:
Project Budget													1,200.0
Amount expended in current year													372.3
Amount committed to funding for social and infrastructure improvement projects														PEN 100.0	$ 33.0
Amount paid-out for development projects in the Candarave province												PEN 445.0	$ 143.0
MGE
Other commitments:
Number of power plants | item																2
Percentage of supply to third-party energy users									12.00%
MGE | Mexico
Other commitments:
Number of power plants | item										2
Net total capacity (in megawatts) | MW				516.2
Copper | Toquepala Concentrator Expansion | Peru
Other commitments:
Estimated increase in annual production (in tons) | T											100,000
Molybdenum | Toquepala Concentrator Expansion | Peru
Other commitments:
Estimated increase in annual production (in tons) | T											3,100
Enersur | Power purchase agreements
Other commitments:
Term of power purchase agreement related to sale of power plant																	20 years
Electroperu S.A | Power purchase agreements
Other commitments:
Term of power purchase agreement related to sale of power plant		20 years
Purchase agreement, contracted power capacity (in megawatts) | MW		120
Kallpa | Power purchase agreements
Other commitments:
Term of power purchase agreement related to sale of power plant	10 years
Purchase agreement, contracted power capacity (in megawatts) | MW	120