Summary of Significant Accounting Policies Regulatory Assets Disclosure (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014		Dec. 31, 2012
Regulatory Assets [Line Items]
Regulatory disallowance on insurance proceeds	$ 15,000
Regulatory Assets, Noncurrent	348,421		368,908		285,046
Regulatory Assets, Current	67,702		68,562		27,834
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	1,117	[1]	3,515	[1]	96	[1]
Regulatory Assets, Current	23,242	[1]	29,889	[1]	1,191	[1]
Asset Recoverable Gas Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	4,334		5,971		6,541
Regulatory Assets, Current	19,653		21,794		14,168
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	197,601		201,845		123,399
Pension Balancing [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	35,374	[2]	32,541	[2]	27,328	[2]
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	50,175	[3],[4]	58,859	[3],[4]	63,517	[3],[4]
Other Regulatory [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	15,053	[5]	18,750	[5]	15,158	[5]
Regulatory Assets, Current	$ 24,807	[5]	$ 16,879	[5]	$ 12,475	[5]

[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 being unrecognized until amounts are collected in rates.

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

[4] 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.

[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.