Commitments and Contingencies (details) (USD $)	6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	$ 37,574,000	$ 35,457,000	$ 31,900,000
Other non-current liabilities	70,127,000	70,942,000	60,385,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	326,081,000	348,897,000	329,197,000
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
Cumulative Environmental Costs Recognized	107,200,000
Cumulative Environmental Costs Recognized Prior To Regulatory Order	4,900,000
Environmental Regulatory Assets Noncurrent	120,285,000	114,312,000	109,324,000
Environmental Regulatory Assets Noncurrent Cumulative Costs Paid	49,400,000
Environmental Regulatory Assets Noncurrent Accrued Costs	59,600,000
Environmental Regulatory Assets Noncurrent Accrued Interest	16,700,000
Environmental Regulatory Assets Noncurrent Cumulative Costs Expensed	5,400,000
Gasco Source Control Liability	11,800,000
Gasco Other Liabilities	37,800,000
Environmental Noncurrent Liabilities	45,960,000	46,621,000	51,548,000
Environmental Current Liabilities	13,595,000	14,396,000	10,633,000
Gasco [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	10,593,000	11,366,000	7,996,000
Other non-current liabilities	38,965,000	38,921,000	43,522,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	78,270,000	74,205,000	71,531,000
Siltronic [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	836,000	720,000	724,000
Other non-current liabilities	71,000	201,000	358,000
Other Liabilities	900,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	3,502,000	3,174,000	3,068,000
Portland Harbor [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	2,161,000	2,304,000	1,836,000
Other non-current liabilities	5,426,000	5,784,000	6,875,000
Other Liabilities	7,600,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	35,379,000	33,940,000	32,712,000
Central Service Center [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	5,000	5,000	5,000
Other non-current liabilities	543,000	510,000	510,000
Other Liabilities	500,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	612,000	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	823,000	1,097,000	166,000
Other Liabilities	800,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	2,067,000	2,020,000	1,056,000
Other Environmental [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	0	0	0
Other non-current liabilities	132,000	108,000	117,000
Non Current Environmental Regulatory Assets [Abstract]
Regulatory Assets	$ 455,000	$ 420,000	$ 406,000