Environmental Matters (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014		Dec. 31, 2012
Environmental Activity [Line Items]
OPUC order on environmental remediation cost	To date, the Company has received total environmental insurance proceeds of approximately $150 million as a result of settlements from our litigation that was dismissed in July 2014. Under the Order, one-third of the proceeds recognized in regulatory accounts are applied to costs deferred through 2012 and the remaining two-thirds is applied ratably to costs over the next 20 years. Under the mechanism, the Company will recover the first $5 million of annual expense through an amount that will be collected from customers through a tariff rider. The Company will apply $5 million of insurance (plus interest) to the next portion of environmental expenses each year. Any expenses in excess of the annual $10 million (plus interest from insurance) are fully recoverable through the SRRM, to the extent the utility earns at or below its authorized Return On Equity (ROE). To the extent the Company earns more than its authorized ROE in a year, the Company is required to cover environmental expenses greater than the $10 million (plus interest from insurance proceeds) with those earnings that exceed its authorized ROE. The Company filed its required compliance report regarding implementation of this mechanism on March 31, 2015. The report is subject to review and approval by the OPUC and as such, may require additional or different implementation procedures, which could, among other things, result in additional impacts on earnings.
Regulatory disallowance on insurance proceeds	$ 15,000,000
Deferred environmental charges							95,000,000
Environmental Settlement Insurance Proceeds Received To Date			150,000,000
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	81,097,000		80,123,000		82,261,000
Environmental Current Liabilities	12,760,000		15,384,000		13,068,000
Environmental Regulatory Table [Abstract]
Cash Paid for Environmental Sites	117,005,000	[1]	113,740,000	[1]	106,105,000	[1]
Environmental Remediation Obligations [Abstract]
Portland Harbor draft FS range	$169 million to $1.8 billion
Portland Harbor Number Of Potentially Responsible Parties	more than 100
Gasco Siltronic Sediments draft EE/CA range	$40 million to $350 million
Gasco Siltronic Sediments Project Liability	40,000,000
Gasco Groundwater Source Control construction costs	19,000,000
Gasco Groundwater Source Control Allocated Insurance Proceeds To Constructed Water Treatment Station	2,500,000
Gasco Siltronic Sediments [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	38,379,000		38,019,000		38,584,000
Environmental Current Liabilities	1,572,000		1,767,000		776,000
Portland Harbor Other [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	5,186,000		4,338,000		3,283,000
Environmental Current Liabilities	1,308,000		1,934,000		1,408,000
Gasco Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	36,833,000		37,117,000		39,482,000
Environmental Current Liabilities	8,205,000		9,535,000		8,766,000
Siltronic Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	405,000		348,000		394,000
Environmental Current Liabilities	750,000		957,000		872,000
Central Service Center [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	0		0		224,000
Environmental Current Liabilities	170,000		171,000		70,000
Front Street [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	115,000		122,000		115,000
Environmental Current Liabilities	755,000		1,020,000		1,176,000
Oregon Steel Mills [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	179,000		179,000		179,000
Environmental Current Liabilities	$ 0		$ 0		$ 0

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