INCOME TAXES: (Details 4)	12 Months Ended										12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2012 Peru USD ($)	Dec. 31, 2011 Peru USD ($)	Dec. 31, 2012 Peru Maximum	Dec. 31, 2012 Peru Minimum	Dec. 31, 2012 United States Minera Mexico USD ($)	Dec. 31, 2012 Mexican Operations USD ($)	Dec. 31, 2012 Mexican Operations MXN	Dec. 31, 2009 Mexican Operations	Dec. 31, 2014 Mexican Operations USD ($)	Dec. 31, 2013 Mexican Operations USD ($)
Income Taxes
Corporate flat tax rate (as a percent)											17.50%	17.50%
Excess of financial reporting over tax basis for stock in subsidiary										$ 2,600,000,000
Deferred tax liability potentially remitted foreign earnings										41,300,000
Foreign earnings potentially repatriated										425,000,000
Special mine tax (as a percent)								8.40%	2.00%
Operating income margin (as a percent)						10.00%
Increment in operating income margin (as a percent)								85.00%	5.00%
Increase in special mining tax rate for each 5% increase up to 85% increase in operating income margin (as a percent)						0.40%
Provision for special mining tax						49,600,000	16,400,000
Amortization period of tax liability													5 years
Deferred balance of taxes to be paid											300,000,000	27,000,000		9,000,000	18,000,000
Mexican tax rate (as a percent)	28.00%	29.00%	30.00%	30.00%	30.00%
Changes in unrecognized tax benefits
Unrecognized tax benefits, opening balance			70,600,000	75,700,000	30,700,000
Gross increases tax positions in prior period			39,700,000	21,600,000	46,300,000
Gross decreases tax positions in prior period			200,000	(26,800,000)	(1,800,000)
Gross increases current-period tax positions			110,700,000	100,000	500,000
Net increase / decrease			150,600,000	(5,100,000)	45,000,000
Unrecognized tax benefits, ending balance			221,200,000	70,600,000	75,700,000
Amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate			221,200,000	70,600,000
Accrued interest and penalties included in liability for uncertain tax positions					$ 8,000,000