Summary of Significant Accounting Policies Regulatory Assets Disclosure (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory disallowance on insurance proceeds		$ 15,000
Regulatory Assets, Noncurrent		342,806	$ 368,908	$ 267,248
Regulatory Assets, Current		63,016	68,562	38,265
Deferred environmental charges					$ 95,000
After-tax regulatory disallowance on insurance proceeds		9,100
interest income from deferred environmental expenses		5,300
Unrealized Loss On Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	[1]	1,077	3,515	191
Regulatory Assets, Current	[1]	15,017	29,889	1,466
Asset Recoverable Gas Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent		2,472	5,971	3,768
Regulatory Assets, Current		19,070	21,794	19,268
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent		193,356	201,845	120,942
Pension Balancing [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	[2]	38,255	32,541	28,997
Income Tax Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent		44,767	47,427	49,007
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	[3],[4]	49,917	58,859	52,117
Other Regulatory [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	[5]	12,962	18,750	12,226
Regulatory Assets, Current	[5]	$ 28,929	$ 16,879	$ 17,531

[1] Unrealized gains or losses on derivatives are non-cash items and, therefore, do not earn a rate of return or a carrying charge. These amounts are recoverable through utility rates as part of the annual Purchased Gas Adjustment (PGA) mechanism when realized at settlement.

[2] The deferral of certain pension expenses above or below the amount set in rates was approved by the Public Utility Commission of Oregon (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.

[3] Environmental costs relate to specific sites approved for regulatory deferral by the OPUC and Washington Utilities and Transportation Commission (WUTC). In Oregon, we earn a carrying charge on cash amounts paid, whereas amounts accrued but not yet paid do not earn a carrying charge until expended. We also accrue a carrying charge on insurance proceeds for amounts owed to customers. In Washington, a carrying charge related to deferred amounts will be determined in a future proceeding. See Note 13.

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

[5] These balances primarily consist of deferrals and amortizations under approved regulatory mechanisms. The accounts being amortized typically earn a rate of return or carrying charge.