Commitments and Contingencies (details) (USD $)	9 Months Ended
Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	$ 33,609,000	$ 35,457,000	$ 28,074,000
Other non-current liabilities	68,705,000	70,942,000	62,069,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	328,757,000	348,897,000	339,786,000
Environmental Remediation Obligations Abstract
Loss Contingency Range Of Possible Loss	Based on the information currently available for groundwater source control at the Gasco site and our current assumptions regarding remediation, we have estimated a range of liability between $11 million and $30 million
Wutc Environmental Deferral Start Date	January 26, 2011
Cumulative Environmental Costs Recognized	107,700,000
Cumulative Environmental Costs Recognized Prior To Regulatory Order	4,900,000
Environmental Regulatory Assets Noncurrent	122,454,000	114,312,000	111,931,000
Environmental Regulatory Assets Noncurrent Cumulative Costs Paid	51,800,000
Environmental Regulatory Assets Noncurrent Accrued Costs	58,000,000
Environmental Regulatory Assets Noncurrent Accrued Interest	18,100,000
Environmental Regulatory Assets Noncurrent Cumulative Costs Expensed	5,400,000
Gasco Source Control Liability	11,800,000
Gasco Other Liabilities	36,600,000
Environmental Current Liabilities	13,289,000	14,396,000	11,273,000
Environmental Noncurrent Liabilities	44,711,000	46,621,000	51,125,000
Gasco [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	10,389,000	11,366,000	7,738,000
Other non-current liabilities	38,051,000	38,921,000	43,597,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	79,823,000	74,205,000	72,531,000
Siltronic [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	721,000	720,000	746,000
Other non-current liabilities	114,000	201,000	275,000
Other Liabilities	800,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	3,535,000	3,174,000	3,120,000
Portland Harbor [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	2,174,000	2,304,000	2,712,000
Other non-current liabilities	5,122,000	5,784,000	5,594,000
Other Liabilities	7,300,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	35,889,000	33,940,000	33,316,000
Central Service Center [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	5,000	5,000	5,000
Other non-current liabilities	530,000	510,000	510,000
Other Liabilities	500,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	610,000	553,000	551,000
Front Street [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	0	1,000	72,000
Other non-current liabilities	765,000	1,097,000	1,039,000
Other Liabilities	800,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	2,130,000	2,020,000	2,000,000
Other Environmental [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	0	0	0
Other non-current liabilities	129,000	108,000	110,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	$ 467,000	$ 420,000	$ 413,000

Cumulative costs recognized for known or estimated future costs arising from requirements to perform activities to remediate one or more sites.

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