Note 12. Fair Value Measurement (Detail) - Schedule of assets and liabilities accounted for at fair value on a recurring basis (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Trade accounts receivable:
Receivables from provisional concentrate sales	$ 6,445	$ 9,313
Restricted cash balances:
Total assets	309,413	314,998
Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents:
Money market funds and other bank deposits	278,504	266,463
Available for sale securities:
Equity securities – mining industry	3,584	3,923
Restricted cash balances:
Certificates of deposit and other bank deposits	866	866
Fair Value, Inputs, Level 2 [Member]
Trade accounts receivable:
Receivables from provisional concentrate sales	5,849	10,996
Restricted cash balances:
Base metal forward contracts	$ 20,610	$ 32,750

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This element represents the fair value of assets categorized as other which are not in and of themselves material enough to require separate disclosure.

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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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Total common and preferred stock (which is not mandatorily redeemable, redeemable at the option of the holder, or in any other way classified as liability) equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for equity securities formerly categorized as available-for-sale or held-to-maturity which the entity held as of the date it opted to account for such securities at fair value. An enterprise may also categorize such a security as trading without the intent to sell it in the near term assuming the decision to categorize the security as trading occurred at acquisition.

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