Concentrate Sale Settlements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Deferred Revenue Arrangement
Smelter refining fees, treatment charges and penalties	$ 3.1	$ 3.2	$ 5.8	$ 6.1
Settlement of Provisional Invoices
Deferred Revenue Arrangement
Increase (decrease) in sales from mark-to-market adjustments	$ 0.2	(1.8)	(0.1)	(2.5)
Fair Value
Deferred Revenue Arrangement
Increase (decrease) in sales from mark-to-market adjustments		$ (0.9)	$ (0.1)	$ (2.1)