The current portion of the aggregate tax effects as of the balance sheet date 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; after deducting the allocated valuation allowance, if any, to reduce such amount to net realizable value. Deferred tax liabilities and assets are classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, are classified according to the expected reversal date of the temporary difference. An unrecognized tax benefit that is directly related to a position taken in a tax year that results in a net operating loss carryforward is presented as a reduction of the related deferred tax asset.

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The tax effect as of the balance sheet date of the amount of future tax deductions arising from unused alternative minimum tax credit carryforwards; a tax credit carryforward is the amount by which tax credits available for utilization exceeded statutory limits on inclusion in historical filings, and which can only be utilized if sufficient tax-basis income is generated in future periods and providing tax laws continue to allow such utilization.

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- Definition

Represents the noncurrent portion of 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 noncurrent taxable temporary difference is a difference between the tax basis and the carrying amount of a noncurrent asset or liability in the financial statements prepared in accordance with generally accepted accounting principles. In a classified statement of financial position, an enterprise separates deferred tax liabilities and assets into a current amount and a noncurrent amount. Deferred tax liabilities and assets are classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, are classified according to the expected reversal date of the temporary difference.

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- Definition

The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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- Definition

This element represents the amount of interest expense accrued as of the date of the statement of financial position for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity.

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Income Taxes (Details) (USD $)	12 Months Ended
Income Taxes (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Tax Contingency
Deferred income taxes	$ 13,779,000	$ 32,342,000
Deferred income taxes, noncurrent	185,450,000	329,207,000
Unrecognized Tax Benefits Maximum Estimated Reductions Resulting from Expiration of Applicable Statute of Limitations in Next 12 Months	2,700,000
Uncertain income tax position accruals net of interest expense	500,000	100,000	800,000
Accrued interest recognized due to uncertain tax positions	800,000	800,000
Federal
Income Tax Contingency
Tax credit carryforwards, alternative minimum tax	800,000
EOR tax credit \| Federal
Income Tax Contingency
Tax credit carryforwards	11,100,000
California \| State
Income Tax Contingency
Tax credit carryforwards, alternative minimum tax	700,000
California \| EOR tax credit \| State
Income Tax Contingency
Tax credit carryforwards	13,500,000
Colorado \| Enterprise zone income tax credits \| State
Income Tax Contingency
Tax credit carryforwards	$ 2,500,000