COMMITMENTS AND CONTINGENCIES: - Litigation Matters (Details) $ in Millions		1 Months Ended					9 Months Ended	12 Months Ended
	Oct. 04, 2016 shares	Mar. 31, 2015 item	Mar. 31, 2012 item	May 31, 2011 item	Aug. 31, 2009 USD ($)	Apr. 30, 1996 person	Sep. 30, 2016 PEN ha item lawsuit plaintiff item / shares	Dec. 31, 2012 item	Dec. 31, 2005 item	Dec. 31, 1992	Dec. 31, 1978	Dec. 31, 1971	Sep. 23, 2015 shares
Tia Maria
Litigation Matter
Area of mining concession (in hectares) | ha							32,989.64
Number of lawsuits | lawsuit							4
Virgen Maria
Litigation Matter
Area of mining concession (in hectares) | ha							943.72
Percentage of mining concession							2.90%
Purchase price of shares paid to former stockholders | $					$ 2
Garcia Ataucuri and Others against SCC's Peruvian Branch
Litigation Matter
Number of former Branch workers		104		216
Armando Cornejo Flores Against SCC Peruvian Branch former workers
Litigation Matter
Number of former Branch workers			37				5
Garcia Ataucuri litigation
Litigation Matter
Number of plaintiffs involved in lawsuits filed | plaintiff							800
Mexico Generadora de Energia S. de R.L. ("MGE") | Controladora de Infraestructura Energetica Mexico, S. A. de C. V.
Litigation Matter
Percentage of interest acquired			99.999%
Peru
Litigation Matter
Statutory participation of mine workers in pre-tax profit (as a percent)										8.00%		10.00%
Statutory participation of mine workers in pre-tax profit paid in cash (as a percent)										100.00%	4.00%	40.00%
Statutory participation of mine workers in pre-tax profit received as equity interest of enterprise (as a percent)												60.00%
Percentage of pre-tax profits delivered as "labor shares"											5.50%
Peru | Garcia Ataucuri and Others against SCC's Peruvian Branch
Litigation Matter
Number of former employees who filed the complaint | person						900
Damages sought by the plaintiff (includes old soles and labor shares)							38,763,806.80
Damages sought by the plaintiff | PEN							PEN 3.876380680
Face value of one labor share | item / shares							100
Labor shares issued by the Branch (as a percent)							100.00%
Plaintiffs do not represent the percent of SCC's eligible employees							100.00%
Soles de oro equivalent to today's one sol							1,000,000,000
Number of shares seized as security for damages sought (in shares) | shares													10,501,857
Labor share exchange ratio	10
Investment shares exchange ratio	1,000
Number of labor shares converted to investment shares | shares	1,980
Peru | Labor Matters
Litigation Matter
Percentage of labor unionized							74.00%
Total number of workers							3,366
Number of labor unions							5
Number of labor unions represent majority of workers							1
Number of labor unions other than majority workers unions							4
Term of agreement							3 years
Annual salary increase (as a percent)							5.00%
Mexico | Mexico Generadora de Energia S. de R.L. ("MGE")
Litigation Matter
Number of power plants								2	2
Mexico | Mexico Generadora de Energia S. de R.L. ("MGE") | Controladora de Infraestructura Energetica Mexico, S. A. de C. V.
Litigation Matter
Percentage of interest acquired								99.999%