Subsequent Event (Details)	12 Months Ended
Dec. 31, 2015
Subsequent Events [Abstract]
Subsequent Event, Description	On January 27, 2016, the Public Utility Commission of Oregon (OPUC) issued an Order (2016 OPUC Order) deciding the three issues raised as a result of our required Site Remediation Recovery Mechanism (SRRM) compliance filing. The OPUC ordered: (1) the disallowance of $2.8 million of interest earned on the previously disallowed environmental expenditures amounts; (2) the allocation of 96.68% of environmental remediation costs for all environmental sites to Oregon; and (3) our treatment of $13.8 million of expenses put into the SRRM amortization account was correct and in compliance with prior OPUC orders. Under a prior OPUC order we were required to forgo collection of $15 million out of approximately $95 million of environmental remediation expenses and associated carrying costs that the Company had deferred through 2012 based on the OPUC’s determination of how an earnings test should apply to amounts deferred from 2003 to 2012, with adjustments for other factors the OPUC deemed relevant. We recognized interest of approximately $2.8 million on the $15 million charge after that time. This interest is shown as a regulatory asset in our financial statements, and the disallowance will result in a $2.8 million pre-tax charge in the first quarter of 2016. Consistent with our accounting policy for recognition of regulatory actions, we recognize the financial impacts in the period in which the order was received. With respect to allocation of 96.68% of environmental remediation costs to Oregon, we currently have a deferral order in Washington to defer environmental costs and insurance proceeds; however, recovery of those costs has not yet been determined. We have deferred costs for certain sites that only served Oregon customers and have, as a result of this order, determined it appropriate to reserve against 3.32% of these deferrals until resolution of recovery in Washington can be determined. The total reserve amount is approximately $0.5 million and will be recorded in the first quarter of 2016 in accordance with the Company’s policy. Consistent with our compliance filing filed in September 2015, the OPUC also ordered the same allocation factors should be applied to insurance proceeds, resulting in the application of 96.68% of the Company’s recovered insurance proceeds to Oregon. With respect to a third issue raised in the proceeding by a customer group that the Company should not be allowed to apply and recover portions of the SRRM amounts in 2013, 2014 and 2015 because that would constitute retroactive ratemaking, the OPUC ordered in the Company’s favor. The OPUC ordered our treatment of $13.8 million of expenses put into the SRRM amortization account, to be amortized over five years, was correct and complied with the original order. For more information regarding our SRRM, see Note 15.

Subsequent Event (Details)

12 Months Ended

Dec. 31, 2015

On January 27, 2016, the Public Utility Commission of Oregon (OPUC) issued an Order (2016 OPUC Order) deciding the three issues raised as a result of our required Site Remediation Recovery Mechanism (SRRM) compliance filing. The OPUC ordered: (1) the disallowance of $2.8 million of interest earned on the previously disallowed environmental expenditures amounts; (2) the allocation of 96.68% of environmental remediation costs for all environmental sites to Oregon; and (3) our treatment of $13.8 million of expenses put into the SRRM amortization account was correct and in compliance with prior OPUC orders. Under a prior OPUC order we were required to forgo collection of $15 million out of approximately $95 million of environmental remediation expenses and associated carrying costs that the Company had deferred through 2012 based on the OPUC’s determination of how an earnings test should apply to amounts deferred from 2003 to 2012, with adjustments for other factors the OPUC deemed relevant. We recognized interest of approximately $2.8 million on the $15 million charge after that time. This interest is shown as a regulatory asset in our financial statements, and the disallowance will result in a $2.8 million pre-tax charge in the first quarter of 2016. Consistent with our accounting policy for recognition of regulatory actions, we recognize the financial impacts in the period in which the order was received. With respect to allocation of 96.68% of environmental remediation costs to Oregon, we currently have a deferral order in Washington to defer environmental costs and insurance proceeds; however, recovery of those costs has not yet been determined. We have deferred costs for certain sites that only served Oregon customers and have, as a result of this order, determined it appropriate to reserve against 3.32% of these deferrals until resolution of recovery in Washington can be determined. The total reserve amount is approximately $0.5 million and will be recorded in the first quarter of 2016 in accordance with the Company’s policy. Consistent with our compliance filing filed in September 2015, the OPUC also ordered the same allocation factors should be applied to insurance proceeds, resulting in the application of 96.68% of the Company’s recovered insurance proceeds to Oregon. With respect to a third issue raised in the proceeding by a customer group that the Company should not be allowed to apply and recover portions of the SRRM amounts in 2013, 2014 and 2015 because that would constitute retroactive ratemaking, the OPUC ordered in the Company’s favor. The OPUC ordered our treatment of $13.8 million of expenses put into the SRRM amortization account, to be amortized over five years, was correct and complied with the original order. For more information regarding our SRRM, see Note 15.