Environmental Matters (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Environmental Activity [Line Items]
Remediation recovery percentage in Oregon		96.68%
Loss Contingency Range Of Possible Loss Portland Harbor		$791 million to $2.45 billion
Portland Harbor Number Of Potentially Responsible Parties		more than 100
Loss Contingency Range Of Possible Loss Gasco Siltronic		$44.9 million to $350 million
Gasco Siltronic Sediments Project Liability		$ 44,900,000.0
Gasco Groundwater Source Control construction costs		19,000,000.0
Gasco Groundwater Source Control Allocated Insurance Proceeds To Constructed Water Treatment Station		2,500,000
Front Street liability for studies and design costs		1,300,000
SRRM pre-tax regulatory disallowance		15,000,000
Deferred environmental charges		95,000,000
Interest disallowed on SRRM regulatory disallowance		2,800,000
Oregon allocated insurance proceeds		93,000,000
Deferred remediation expense to be collected		8,400,000
Annual tariff rider collection		5,000,000
Environmental Settlement Insurance Proceeds Received To Date		150,000,000
Annual insurance proceeds to appy against remediation costs		5,000,000
Insurance proceeds applied to prudently incurred remediation costs		53,200,000
Environmental Regulatory Table [Abstract]
Cash Paid for Environmental Sites		124,325,000	$ 113,740,000
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities		16,931,000	15,384,000
Environmental Noncurrent Liabilities		108,095,000	80,123,000
Regulatory Assets, Current		69,178,000	68,562,000
Regulatory Assets, Noncurrent		370,711,000	368,908,000
Minimum [Member]
Environmental Activity [Line Items]
Front Street Remedial Costs		7,600,000
Maximum [Member]
Environmental Activity [Line Items]
Front Street Remedial Costs		12,900,000
Gasco Siltronic Sediments [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities		2,229,000	1,767,000
Environmental Noncurrent Liabilities		42,641,000	38,019,000
Portland Harbor Other [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities		1,972,000	1,934,000
Environmental Noncurrent Liabilities		5,073,000	4,338,000
Gasco Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities		10,599,000	9,535,000
Environmental Noncurrent Liabilities		52,117,000	37,117,000
Siltronic Upland [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities		951,000	957,000
Environmental Noncurrent Liabilities		337,000	348,000
Central Service Center [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities		25,000	171,000
Environmental Noncurrent Liabilities		0	0
Front Street [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities		1,155,000	1,020,000
Environmental Noncurrent Liabilities		7,748,000	122,000
Oregon Steel Mills [Member]
Accrual for Environmental Loss Contingencies [Abstract]
Environmental Current Liabilities		0	0
Environmental Noncurrent Liabilities		179,000	179,000
Environmental Restoration Costs [Member]
Environmental Regulatory Table [Abstract]
Environmental Regulatory Assets Noncurrent	[1]	85,854,000	58,859,000
Accrual for Environmental Loss Contingencies [Abstract]
Regulatory Assets, Current	[2],[3]	9,270,000	0
Regulatory Assets, Noncurrent	[3]	$ 76,584,000	$ 58,859,000

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

[2] Current environmental costs represent remediation costs management expects to collect from customers in the next 12 months. Amounts included in this estimate are still subject to a prudence and earnings test review by the OPUC and do not include the $5 million base rate rider. The Oregon amounts are recoverable through utility rates, subject to an earnings test.

[3] Current environmental costs represent remediation costs management expects to collect from customers in the next 12 months. Amounts included in this estimate are still subject to a prudence and earnings test review by the OPUC and do not include the $5 million base rate rider. The amounts allocable to Oregon are recoverable through utility rates, subject to an earnings test. See Note 15.