Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2014
Revenue Recognition
Number of days used for observing average prices of metals	10 days
Building | Minimum
Property, plant and equipment and long-lived asset impairment
Useful life	30 years
Building | Maximum
Property, plant and equipment and long-lived asset impairment
Useful life	40 years
Mining equipment and machinery | Minimum
Property, plant and equipment and long-lived asset impairment
Useful life	3 years
Mining equipment and machinery | Maximum
Property, plant and equipment and long-lived asset impairment
Useful life	8 years
Other furniture and equipment | Minimum
Property, plant and equipment and long-lived asset impairment
Useful life	3 years
Other furniture and equipment | Maximum
Property, plant and equipment and long-lived asset impairment
Useful life	5 years