Summary of Significant Accounting Policies Regulatory Assets Disclosure (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accounting Policies [Abstract]
Public Utilities, Property, Plant and Equipment, Disclosure of Composite Depreciation Rate for Plants in Service	2.80%		2.80%		2.80%
Weighted Average Depreciation Rates Transmission Distribution	2.70%
Weighted Average Depreciation Rates Utility Storage	2.20%
Weighted Average Depreciation Rates General Plant	4.70%
Weighted Average Depreciation Rates Intangible Other	2.90%
Public Utilities, Allowance for Funds Used During Construction, Rate	0.30%		0.30%		0.30%
Outstanding Checks In Accounts Payable	$ 5,500,000		$ 2,800,000
Unbilled Receivables, Current	57,963,000		61,527,000
Inventory - Gas	68,000,000		51,400,000
Inventory - Materials and supplies	9,800,000		9,300,000
Changes In Fair Value As Deferred Regulatory Assets Or Liabilities In Percentage	80% or 90%
Changes In Fair Value Deferred As Income Statement For Contracts Not Qualifying For Hedge Accounting And To Other Comprehensive Income For Contracts Qualifying For Hedge Accounting	20% or 10%
Oregon PGA Deferral Percentage	90.00%		90.00%		90.00%
Washington PGA Deferral Percentage	100.00%		100.00%		100.00%
Deferred Tax Liabilities, Deferred Expense	51,800,000		56,200,000
Regulatory Assets [Line Items]
SRRM pre-tax regulatory disallowance	15
Revenue Taxes	18,800,000		19,000,000		18,400,000
Regulatory Assets, Noncurrent	368,908,000		369,603,000
Regulatory Assets, Current	68,562,000		22,635,000
Unrealized Loss On Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	3,515,000	[1]	615,000	[1]
Regulatory Assets, Current	29,889,000	[1]	1,891,000	[1]
Pension and Other Postretirement Plans Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	201,845,000	[2]	125,855,000	[2]
Pension Balancing [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	32,541,000	[2]	25,713,000	[2]
Other Regulatory [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	18,750,000	[3]	15,377,000	[3]
Regulatory Assets, Current	16,879,000	[3]	16,458,000	[3]
Income Tax Asset [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	47,427,000		51,814,000
Environmental Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	58,859,000	[4]
Asset Recoverable Gas Costs [Member]
Regulatory Assets [Line Items]
Regulatory Assets, Noncurrent	5,971,000	[4]	1,840,000	[4]
Regulatory Assets, Current	$ 21,794,000		$ 4,286,000

[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] Certain utility pension costs are approved for regulatory deferral, including amounts recorded to the pension balancing account, to mitigate the effects of higher and lower pension expenses. Deferred pension costs include an interest component when recognized in net periodic benefit costs. See Note 8.

[3] 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

[4] Environmental costs relate to specific sites approved for regulatory deferral by the OPUC and 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 15.