INTANGIBLE ASSETS: (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Intangible assets
Intangible assets excluding goodwill, gross	$ 139,400,000	$ 136,100,000
Accumulated amortization	(46,200,000)	(43,800,000)
Goodwill	17,000,000	17,000,000
Intangible assets, net	110,219,000	109,300,000
Amortization expense:
Amortization expense	2,400,000	2,200,000	2,100,000
Estimated amortization expense:
2014-2018	9,100,000
Average annual	1,800,000
Mining concessions
Intangible assets
Intangible assets excluding goodwill, gross	121,200,000	121,200,000
Mine engineering and development studies
Intangible assets
Intangible assets excluding goodwill, gross	6,000,000	6,000,000
Software
Intangible assets
Intangible assets excluding goodwill, gross	$ 12,200,000	$ 8,900,000