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Note 12 - Fair Value Measurement (Tables) | 9 Months Ended
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Sep. 30, 2013
Fair Value Disclosures [Abstract] |
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Table Text Block] |
Description |  | Balance at September 30, 2013 |  |  | Balance at December 31, 2012 |  | Input Hierarchy Level
Assets: |  |  |  |  |  |  |  |  |
Cash and cash equivalents: |  |  |  |  |  |  |  |  |
Money market funds and other bank deposits |  | $ | 237,836 |  |  | $ | 190,984 |  | Level 1
Available for sale securities: |  |  |  |  |  |  |  |  |
Equity securities – mining industry |  |  | 8,364 |  |  |  | 9,614 |  | Level 1
Trade accounts receivable: |  |  |  |  |  |  |  |  |
Receivables from provisional concentrate sales |  |  | 34,481 |  |  |  | 17,555 |  | Level 2
Restricted cash balances: |  |  |  |  |  |  |  |  |
Certificates of deposit and other bank deposits |  |  | 5,378 |  |  |  | 871 |  | Level 1
Derivative contracts: |  |  |  |  |  |  |  |  |
Base metal forward contracts |  |  | 18,712 |  |  |  | 5,606 |  | Level 2
Total assets |  | $ | 304,771 |  |  | $ | 224,630 |  |
Liabilities: |  |  |  |  |  |  |  |  |
Derivative contracts: |  |  |  |  |  |  |  |  |
Base metal forward contracts |  | $ | — |  |  | $ | 2,483 |  | Level 2

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- Definition Tabular disclosure of the inputs and valuation techniques used to measure fair value, and a discussion of changes in valuation techniques and related inputs, if any, applied during the period to each separate class of assets, liabilities, and financial instruments classified in shareholders' equity that are measured on a recurring and/or nonrecurring basis. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258 + Details
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