Note 11 - Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Unsettled Sales and Forecasted Future Concentrate Contracts [Member] \| Other Current Assets [Member]
Note 11 - Derivative Instruments (Details) [Line Items]
Derivative Asset, Current	$ 6.8
Derivative Liability, Current	0.9
Unsettled Sales and Forecasted Future Concentrate Contracts [Member] \| Other Noncurrent Assets [Member]
Note 11 - Derivative Instruments (Details) [Line Items]
Derivative Asset, Noncurrent	7.5
Derivative Liability, Noncurrent	0.2
Unsettled Concentrate Sales Contracts [Member]
Note 11 - Derivative Instruments (Details) [Line Items]
Derivative, Gain on Derivative	0.3
Forecasted Future Concentrate Contracts [Member] \| Gains Realized on Settled Contracts [Member]
Note 11 - Derivative Instruments (Details) [Line Items]
Derivative, Gain on Derivative	1.9
Forecasted Future Concentrate Contracts [Member]
Note 11 - Derivative Instruments (Details) [Line Items]
Derivative, Gain on Derivative	$ 5.8

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References+ Details