Note 12 - Fair Value Measurement (Details) - Assets and Liabilities Accounted for at Fair Value (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Trade accounts receivable:
Receivables from provisional concentrate sales	$ 6,792us-gaap_OtherReceivables	$ 4,689us-gaap_OtherReceivables
Restricted cash balances:
Total assets	244,511us-gaap_OtherAssetsFairValueDisclosure	246,544us-gaap_OtherAssetsFairValueDisclosure
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents:
Money market funds and other bank deposits	209,665	212,175
Available for sale securities:
Equity securities – mining industry	4,920	7,019
Restricted cash balances:
Certificates of deposit and other bank deposits	883	5,217
Fair Value, Inputs, Level 2 [Member]
Trade accounts receivable:
Receivables from provisional concentrate sales	17,696	17,672
Derivative contracts:
Base metal forward contracts	$ 11,347	$ 4,461

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A savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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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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