COMMITMENTS AND CONTINGENCIES: (Details) MXN in Millions, $ in Millions								1 Months Ended	3 Months Ended		6 Months Ended		9 Months Ended			12 Months Ended
	Aug. 07, 2015 item	Mar. 02, 2015 MXN item	Mar. 02, 2015 USD ($) item	Sep. 15, 2014 MXN	Sep. 15, 2014 USD ($)	Aug. 29, 2014	Aug. 06, 2014 km m³	Mar. 31, 2014	Sep. 30, 2015 USD ($) item	Jun. 30, 2015 item	Jun. 30, 2015 item	Dec. 31, 2014 item	Sep. 30, 2015 MXN item / m³ item	Sep. 30, 2015 USD ($) item / m³ item	Sep. 30, 2014 USD ($)	Dec. 31, 2013	Dec. 31, 2011 category person
Environmental costs
Environmental capital investment | $														$ 76.2	$ 113.4
Amount of administrative fines and sanctions (in pesos)		MXN 23.5	$ 1.7
Number of collective action lawsuits											6	6
Number of Constitutional action lawsuits									3	3
Number of lawsuits dismissed	2
Number of subsidiaries against which lawsuits were filed													2	2
Maximum
Environmental costs
Number of zones													5	5
Minimum
Environmental costs
Number of zones													2	2
Buenavista del Cobre, S.A. de C.V
Environmental costs
Volume of copper sulfate solution (in cubic meters) | m³							40,000
Distance of pond under construction from mine (in kilometers) | km							10
Number of zones													5	5
Amount committed to the Mexican Federal Government to establish a trust (in peso)				MXN 2,000.0	$ 150.0
Amount contributed to the Mexican Federal Government (in peso) | MXN													MXN 1,000.0
Number of administrative proceedings.		4	4
Number of workers hired						1,200
Estimated contingent liability | $									$ 114.8					$ 114.8
Amount already paid | $									$ 39.9					39.9
Amount deposited in the trust (in peso)													MXN 1,000.0	74.9
Number of civil actions seeking damages											7
Peru
Environmental costs
Environmental capital investment | $														$ 60.8	95.9
Period required for ambient air monitoring as per environmental regulation																1 day
Air quality standards level for sulfur dioxide to be maintained when emission is excess than specified as per new environmental regulation (in micrograms per cubic meter) | item / m³													80	80
Number of atmospheric basins established that require further attention													3	3
Number of months for identification of contaminated sites and around in facilities								12 months
Period for preparation of decontamination plan								P24M
Period of extension for preparation of decontamination plan								1 year
Number of days in which results of soil confirmation tests are to be presented to authorities								30 days
Peru | Maximum
Environmental costs
Revised air quality standards for sulfur dioxide as per new environmental regulation (in micrograms per cubic meter) | item / m³													20	20
Mexico
Environmental costs
Environmental capital investment | $														$ 15.4	$ 17.5
Number of categories of collective actions | category																	3
Minimum number of people claiming injury due to collective action initiative in Civil Federal Procedures Code (CFPC) | person																	30
Francisco Garcia Enriquez
Environmental costs
Number of Constitutional action lawsuits									2	2