COMMITMENTS AND CONTINGENCIES: (Details 3)	12 Months Ended	3 Months Ended	0 Months Ended		12 Months Ended	3 Months Ended
	Dec. 31, 1997	Mar. 31, 2013 Tia Maria Peruvian operations USD ($) T	Feb. 08, 2013 Toquepala Concentrator Expansion Peruvian operations USD ($) item	Feb. 08, 2013 Toquepala Concentrator Expansion Peruvian operations PEN	Dec. 31, 2005 MGE item	Mar. 31, 2013 MGE Mexican Operations USD ($) item
Other commitments:
Estimated annual production of copper cathodes (in tons)		120,000
Term of power purchase agreement related to sale of power plant	20 years
Total budget for the project		$ 1,000,000,000
Total spending for the project		495,600,000
Equipment reassigned to other operations, carrying value		196,500,000
Number of provinces for which final agreement reached			1	1
Number of provinces neighboring the Toquepala unit			3	3
Amount committed to funding for development projects in the Candarave province			100,000,000	255,000,000
Number of power plants					2	2
Estimated monthly capacity charge of power under power purchase agreement						$ 4,300,000