Commitments and Contingencies (details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Commitments [Abstract]
Unrecorded Unconditional Purchase Obligation, Purchases	$ 94,200,000	$ 91,400,000	$ 84,600,000
Unrecorded Unconditional Purchase Obligation Offsetting Sales	3,100,000	4,200,000	4,200,000
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	41,597,000	35,457,000
Other non-current liabilities	76,265,000	70,942,000
Other Liabilities	72,700,000
Environmental Remediation Obligations Abstract
Loss Contingency Range Of Possible Loss	between $11 million and $30 million
Gasco Source Control Liability	12,000,000
Gasco Other Liabilities	49,200,000
Wutc Environmental Deferral Start Date	January 26, 2011
Cumulative Environmental Costs Recognized	124,800,000
Cumulative Environmental Costs Recognized Prior To Regulatory Order	4,900,000
Environmental Regulatory Assets Noncurrent	105,700,000
Damages Sought On Environmental Claims	50,000,000
Gas Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	98,534,000
Unrecorded Unconditional Purchase Obligation, Due within Two Years	18,331,000
Unrecorded Unconditional Purchase Obligation, Due within Three Years	15,290,000
Unrecorded Unconditional Purchase Obligation, Due within Four Years	5,651,000
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	137,806,000
Less: Amount representing interest	682,000
Total At Present Value	137,124,000
Pipeline Capacity Purchase Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	91,027,000
Unrecorded Unconditional Purchase Obligation, Due within Two Years	87,983,000
Unrecorded Unconditional Purchase Obligation, Due within Three Years	82,898,000
Unrecorded Unconditional Purchase Obligation, Due within Four Years	72,316,000
Unrecorded Unconditional Purchase Obligation, Due within Five Years	61,358,000
Unrecorded Unconditional Purchase Obligation, Due after Five Years	287,541,000
Unrecorded Unconditional Purchase Obligation	683,123,000
Less: Amount representing interest	99,252,000
Total At Present Value	583,871,000
Pipeline Capacity Release Agreements [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Unrecorded Unconditional Purchase Obligation, Due within One Year	3,464,000
Unrecorded Unconditional Purchase Obligation, Due within Two Years	0
Unrecorded Unconditional Purchase Obligation, Due within Three Years	0
Unrecorded Unconditional Purchase Obligation, Due within Four Years	0
Unrecorded Unconditional Purchase Obligation, Due within Five Years	0
Unrecorded Unconditional Purchase Obligation, Due after Five Years	0
Unrecorded Unconditional Purchase Obligation	3,464,000
Less: Amount representing interest	2,000
Total At Present Value	3,462,000
Gasco [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	16,510,000	11,366,000
Other non-current liabilities	44,697,000	38,921,000
Other Liabilities	61,200,000
Siltronic [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	887,000	720,000
Other non-current liabilities	128,000	201,000
Other Liabilities	1,000,000
Portland Harbor [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	1,089,000	2,304,000
Other non-current liabilities	7,066,000	5,784,000
Other Liabilities	8,200,000
Central Service Center [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	0	5,000
Other non-current liabilities	495,000	510,000
Other Liabilities	500,000
Front Street [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	1,697,000	1,000
Other non-current liabilities	0	1,097,000
Other Liabilities	1,700,000
Other Environmental [Member]
Accrual For Environmental Loss Contingencies [Abstract]
Other current liabilities	0	0
Other non-current liabilities	$ 120,000	$ 108,000