Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative, Gain on Derivative	$ 10,500,000
Summary of Derivative Instruments [Abstract]
Cost of sales	(365,490,000)	(373,298,000)	(355,335,000)
General Discussion of Derivative Instruments and Hedging Activities [Abstract]
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%
Derivative, Loss on Derivative		11,000,000.0
Unrealized Gain On Derivatives	30,600,000
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	200,000	7,200,000
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	33,400,000	2,500,000
Maturity Of Credit Risk Derivatives	Mar. 01, 2017
Derivative Fair Value Of Derivative Net	(33,200,000)	(4,700,000)
Notional Disclosures [Abstract]
Financial Derivative, Nonmonetary Notional Amount	287,475,000	389,225,000
Derivative, Nonmonetary Notional Amount	420,980,000	552,500,000
Notional Amount of Foreign Currency Derivatives	12,230,000	15,002,000
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	(32,784,000)	4,985,000
Less:Amounts deferred to regulatory accounts on balance sheet	32,782,000	(4,964,000)
Total Impact On Earnings	(2,000)	21,000
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Total Comprehensive Income	(382,000)	(300,000)
Less:Amounts deferred to regulatory accounts on balance sheet	382,000	300,000
Total Impact On Earnings	$ 0	$ 0