Note 12. Fair Value Measurement (Detail) - Assets And Liabilities Accounted For At Fair Value (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Restricted cash balances:
Total assets	$ 425,953	$ 322,883
Level1 [Member]
Cash and cash equivalents:
Money market funds and other bank deposits	377,436	283,606
Equity securities – mining industry	4,161	2,668
Restricted cash balances:
Certificates of deposit and other bank deposits	926	10,314
Level2 [Member]
Trade accounts receivable:
Receivables from provisional concentrate sales	43,430	36,295
Derivative contracts:
Base metal forward contracts	$ 11,597	$ 20,794

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Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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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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