Environmental Matters (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2012
Environmental Activity [Line Items]
OPUC order on environmental remediation cost	The Company 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 to costs over the next 20 years. Under the SRRM, the Company will recover the first $5 million of annual expense through an amount that will be collected from Oregon 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 demonstrating the proposed implementation of the Order and SRRM on March 31, 2015. The Company is engaged in discussions with the parties to resolve issues they have raised regarding the compliance filing and expects a determination by the OPUC in the second half of 2015. The compliance filing is subject to final 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. In addition, the Company entered into a settlement regarding the secured account, which is currently pending with the OPUC.
Regulatory disallowance on insurance proceeds	$ 15,000
Deferred environmental charges				$ 95,000
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	80,990	$ 80,123	$ 82,045
Environmental Current Liabilities	10,186	15,384	11,337
Environmental Settlement Insurance Proceeds Received To Date		150,000
Environmental Regulatory Table [Abstract]
Cash Paid for Environmental Sites	$ 119,403	113,740	108,783
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	$39.9 million to $350 million
Gasco Siltronic Sediments Project Liability	$ 39,900
Gasco Groundwater Source Control construction costs	19,000
Gasco Groundwater Source Control Allocated Insurance Proceeds To Constructed Water Treatment Station	2,500
Gasco Siltronic Sediments [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	38,342	38,019	38,535
Environmental Current Liabilities	1,512	1,767	799
Portland Harbor Other [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	4,941	4,338	3,080
Environmental Current Liabilities	1,208	1,934	1,317
Gasco Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	37,031	37,117	39,553
Environmental Current Liabilities	5,938	9,535	7,152
Siltronic Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	390	348	401
Environmental Current Liabilities	710	957	884
Central Service Center [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	0	0	190
Environmental Current Liabilities	153	171	70
Front Street [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	107	122	107
Environmental Current Liabilities	665	1,020	1,115
Oregon Steel Mills [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities	179	179	179
Environmental Current Liabilities	$ 0	$ 0	$ 0