Note 12 - Fair Value Measurement (Details) - Assets and Liabilities Accounted for at Fair Value (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Trade accounts receivable:
Receivables from provisional concentrate sales	$ 5,215us-gaap_OtherReceivables	$ 6,792us-gaap_OtherReceivables
Derivative contracts:
Total assets	243,045us-gaap_OtherAssetsFairValueDisclosure	244,511us-gaap_OtherAssetsFairValueDisclosure
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents:
Money market funds and other bank deposits	196,231	209,665
Available for sale securities:
Equity securities – mining industry	4,334	4,920
Restricted cash balances:
Certificates of deposit and other bank deposits	883	883
Fair Value, Inputs, Level 2 [Member]
Trade accounts receivable:
Receivables from provisional concentrate sales	27,280	17,696
Derivative contracts:
Metal forward contracts	$ 14,317	$ 11,347

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Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts.

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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. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Fair value portion of other assets.

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Carrying amounts due as of the balance sheet date from parties or arising from transactions not otherwise specified in the taxonomy.

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Fair value of investments in trading equity securities and other forms of trading securities that provide ownership interests.

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