COMMITMENTS AND CONTINGENCIES: - Labor matters (Details)	1 Months Ended								3 Months Ended			9 Months Ended
	Nov. 30, 2019 PEN (S/)	Nov. 30, 2019 USD ($)	May 31, 2019 PEN (S/)	May 31, 2019 USD ($)	Mar. 31, 2019 PEN (S/) item	Mar. 31, 2019 USD ($) item	Aug. 31, 2018 USD ($) item	Jun. 30, 2018	Dec. 31, 2018 PEN (S/)	Sep. 30, 2018 PEN (S/)	Sep. 30, 2018 USD ($)	Sep. 30, 2020 USD ($) item employee	Aug. 22, 2018 USD ($)
Labor Matters
Labor matters
Annual salary increase (as a percent)	5.00%	5.00%	5.50%	5.50%
Labor Matters | Year One Collective Bargaining Agreement
Labor matters
Term of agreement			1 year	1 year
Labor expense	S/ 45,000	$ 13,300	S/ 16,000	$ 4,800
Labor Matters | Year Three Collective Bargaining Agreement
Labor matters
Term of agreement	3 years	3 years
Peru | Labor Matters
Labor matters
Percentage of labor unionized												65.50%
Total number of workers | employee												4,790
Number of labor unions												6
Number of labor unions represent majority of workers												1
Number of labor unions other than majority workers unions												5
Term of agreement							3 years	3 years
Annual salary increase (as a percent)					5.00%	5.00%			5.00%	5.00%	5.00%
Labor expense					S/ 45,000	$ 13,600	$ 13,600		S/ 45,000	S/ 45,000	$ 13,600
Number of additional unions					1	1	3
Mexico | San Martin
Labor matters
Budgeted cost for rehabilitation of mine | $													$ 97,700,000
Total expense incurred on rehabilitation of mine till date | $												$ 83,900,000