Note 5. Income Taxes (Detail) - Components of the Net Deferred Tax Asset (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred tax assets:
Deferred Tax Asset	$ 192,516	$ 235,469
Valuation allowance	(22,895)	(19,073)
Total deferred tax assets	169,621	216,396
Deferred tax liabilities:
Deferred Tax Liability	(53,783)	(29,037)
Net deferred tax asset	115,838	187,359
Unrealized (Gain) Loss On Derivatives Contracts [Member]
Deferred tax liabilities:
Deferred Tax Liability	(13,293)
Properties, Plants, And Equipment [Member]
Deferred tax liabilities:
Deferred Tax Liability	(40,490)	(29,037)
Accrued Reclamation Costs [Member]
Deferred tax assets:
Deferred Tax Asset	62,225	129,687
Deferred Exploration [Member]
Deferred tax assets:
Deferred Tax Asset	18,585	14,596
Foreign Net Operating Loses [Member]
Deferred tax assets:
Deferred Tax Asset	20,234	16,850
Federal Net Operating Loses [Member]
Deferred tax assets:
Deferred Tax Asset	47,875	36,744
State Net Operating Losses [Member]
Deferred tax assets:
Deferred Tax Asset	2,445	924
Tax Credit Carryforwards [Member]
Deferred tax assets:
Deferred Tax Asset	15,210	10,879
Unrealized Loss [Member]
Deferred tax assets:
Deferred Tax Asset		8,459
Pension And Benefit Obligation [Member]
Deferred tax assets:
Deferred Tax Asset	9,940	3,198
Miscellaneous [Member]
Deferred tax assets:
Deferred Tax Asset	$ 16,002	$ 14,132

The sum of the tax effects as of the balance sheet date of the amounts of all future tax deductions arising from temporary differences between tax basis and generally accepted accounting principles basis recognition of assets, liabilities, revenues and expenses, which can only be deducted for tax purposes when permitted under enacted tax laws ( before the valuation allowance, if any, to reduce such sum amount to net realizable value). Includes any tax benefit realized in deferred tax assets for significant impacts of tax planning strategies.

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For entities that net deferred tax assets and tax liabilities, represents the unclassified net amount of deferred tax assets and liabilities as of the balance sheet date, which result from applying the applicable enacted tax rate to net temporary differences and carryforwards pertaining to assets or liabilities. A temporary difference is a difference between the tax basis of an asset or liability and its carrying amount in the financial statements prepared in accordance with generally accepted accounting principles that will reverse in ensuing periods.

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- Definition

The cumulative amount of all deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. A taxable temporary difference is a difference between the tax basis and the carrying amount of an asset or liability in the financial statements prepared in accordance with generally accepted accounting principles that will result in taxable amounts in one or more future periods.

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- Definition

The amount of the valuation allowance recorded as of the balance sheet date pertaining to the specified deferred tax asset for which an assessment was made that it is more likely than not that all or a portion of such deferred tax asset will not be realized through related deductions on future tax returns.

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