Summary of Significant Accounting Policies Regulatory Assets Disclosure (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 367,692		$ 371,392		$ 328,757
Regulatory Assets, Current	53,891		94,673		76,734
Other Regulatory [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	8,439	[1]	17,402	[1]	14,637	[1]
Regulatory Assets, Current	21,244	[1]	21,865	[1]	19,095	[1]
Unrealized Loss On Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	615	[2]	6,536	[2]	7,429	[2]
Regulatory Assets, Current	17,156	[2]	57,317	[2]	46,651	[2]
Pension Balancing [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	13,134	[3]	6,008	[3]	3,989	[3]
Income Tax Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	58,437		65,264		70,241
Pension and Other Postretirement Benefit Liabilities [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	158,894	[3]	170,512	[3]	110,007	[3]
Regulatory Assets, Current	15,491	[3]	15,491	[3]	10,988	[3]
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	$ 128,173	[4]	$ 105,670	[4]	$ 122,454	[4]

[1] Other primarily consists of deferrals and amortizations under other approved regulatory mechanisms. The accounts being amortized typically earn a rate of return or carrying charge.

[2] 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 mechanism when realized at settlement.

[3] Certain pension costs of the utility are approved for regulatory deferral, including amounts recorded to the pension balancing account, to mitigate the effects of higher and lower pension expenses. Pension costs that are deferred include an interest component when recognized in net periodic benefit costs or earn a rate of return or carrying charge (see Note 8).

[4] Environmental costs are related to those sites that are approved for regulatory deferral. In Oregon we earn a rate of return on amounts paid, whereas amounts accrued but not yet paid do not earn a rate of return or a carrying charge until expended. Environmental costs related to Washington were deferred beginning in 2011, with cost recovery and a carrying charge to be determined in a future proceeding.