Environmental Matters (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2012
Environmental Activity [Line Items]
OPUC order on environmental remediation cost		We 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 OPUC Order, one-third of the proceeds recognized in regulatory accounts and allocated to Oregon sites are applied to costs deferred through 2012 and the remaining two-thirds is applied to costs over the next 20 years. Under the SRRM, we will recover the first $5 million of annual expense through an amount that will be collected from Oregon customers through a tariff rider. We will apply $5 million of insurance (plus interest) to the next portion of environmental expenses each year. Any expenses and interest on 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 our authorized Return On Equity (ROE). To the extent the utility earns more than its authorized ROE in a year, the utility is required to cover environmental expenses and interest on expenses greater than the $10 million (plus interest from insurance proceeds) with those earnings that exceed its authorized ROE. We submitted the required compliance filing demonstrating the proposed implementation of the Order and SRRM in March 2015. In September 2015, as a result of discussions with parties, we withdrew our original compliance filing and submitted a revised filing. In the revised filing, we noted parties may raise issues regarding whether or not interest accrued on the disallowance is recoverable and our interpretation of the state allocation. We are engaged in discussions with the parties to resolve issues they have raised regarding the compliance filing and expect resolution of these matters in the first half of 2016. The revised compliance filing is subject to final review and approval by the OPUC and as a consequence thereof, additional or different implementation procedures could be required, which may, among other things, result in additional impacts on earnings. In addition, we requested clarification from the OPUC regarding the amount of Oregon-allocated insurance proceeds to be held in a secured account. In September 2015, the OPUC resolved the issue by adopting an all-party settlement, which clarified we did not need to obtain a secured account. Instead, the OPUC ordered insurance proceeds used to offset future environmental expenses to accrue interest to be at an interest rate equal to the five-year treasury rate plus 100 basis points. Currently, Oregon-allocated insurance proceeds total approximately $96 million on a pre-tax basis. In Washington, cost recovery and carrying charges on amounts deferred for costs associated with services provided to Washington customers will be determined in a future proceeding. Annually, we review all regulatory assets for recoverability or more often if circumstances warrant. If we should determine all or a portion of these regulatory assets no longer meet the criteria for continued application of regulatory accounting, then we would be required to write off the net unrecoverable balances against earnings in the period such a determination is made.
Regulatory disallowance on insurance proceeds		$ 15,000
Deferred environmental charges					$ 95,000
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities		80,774	$ 80,123	$ 80,567
Environmental Current Liabilities		8,124	15,384	10,653
Environmental Settlement Insurance Proceeds Received To Date			150,000
Anticipated parties request for additional disallowance based on review of accrued interest		3,000
Oregon Allocated Insurance Proceeds		96,000
Regulatory Assets, Noncurrent		333,953	368,908	263,321
Environmental Regulatory Table [Abstract]
Cash Paid for Environmental Sites		$ 121,819	113,740	111,367
Environmental Remediation Obligations [Abstract]
Portland Harbor draft FS range		$791 million to $2.45 billion
Portland Harbor Number Of Potentially Responsible Parties		more than 100
Gasco Siltronic Sediments draft EE/CA range		$39.8 million to $350 million
Gasco Siltronic Sediments Project Liability		$ 39,800
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		38,533	38,019	38,593
Environmental Current Liabilities		1,236	1,767	686
Portland Harbor Other [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities		4,563	4,338	3,198
Environmental Current Liabilities		1,243	1,934	1,060
Gasco Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities		36,795	37,117	37,748
Environmental Current Liabilities		4,510	9,535	7,399
Siltronic Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities		489	348	577
Environmental Current Liabilities		538	957	634
Central Service Center [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities		0	0	173
Environmental Current Liabilities		177	171	70
Front Street [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities		215	122	99
Environmental Current Liabilities		420	1,020	804
Oregon Steel Mills [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Noncurrent Liabilities		179	179	179
Environmental Current Liabilities		0	0	0
Environmental Restoration Costs [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Regulatory Assets	[1],[2]	49,807
Regulatory Assets, Noncurrent	[1],[2]	$ 37,443	$ 58,859	$ 51,861

[1] Includes cash paid, remaining liability, and interest, net of insurance reimbursement and amounts reclassified to utility plant for the water treatment station.

[2] The deferral of certain pension expenses above or below the amount set in rates was approved by the OPUC, with recovery of these deferred amounts through the implementation of a balancing account, which includes the expectation of lower net periodic benefit costs in future years. Deferred pension expense balances include accrued interest at the utility’s authorized rate of return, with the equity portion of interest income recognized when amounts are collected in rates.