Acquisition of El Pilar mine (Details) $ in Thousands		3 Months Ended	9 Months Ended
	Jul. 06, 2015 USD ($) T	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jul. 06, 2015 USD ($)
Acquisition of El Pilar mine
Payment to acquire business, net of cash acquired		$ 100,448	$ 100,448
Recognized amounts of identifiable assets acquired and liabilities assumed
Goodwill		87,000	17,000
Changes in the carrying amount of goodwill
Balance at the beginning of the period			17,000
Goodwill acquired			70,000
Balance at the end of the period		$ 87,000	$ 87,000
Stingray
Acquisition of El Pilar mine
Percentage of ownership acquired (as a percent)				100.00%
Payment to acquire business, net of cash acquired	$ 100,400
Recognized amounts of identifiable assets acquired and liabilities assumed
Financial assets				$ 100
Mineral resources				23,400
Property, plant and equipment				10,500
Financial liabilities				(3,600)
Total identifiable net assets				30,400
Goodwill	70,000			70,000
Goodwill deductible for income tax				0
Changes in the carrying amount of goodwill
Balance at the end of the period	$ 70,000
Stingray | Selling, general and administrative expenses
Acquisition of El Pilar mine
Acquisition related costs				$ 400
Stingray | El Pilar
Acquisition of El Pilar mine
Percentage of interest in mine concession	100.00%
Development investment	$ 300,000
Average annual production of copper cathodes | T	35,000
Mine life with extraction capacity of 35000 tons of copper cathodes	13 years