Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Derivative [Line Items]
Financial Derivative, Nonmonetary Notional Amount	295,125,000	302,020,000	389,225,000
Physical Derivative, Nonmonetary Notional Amount	875,150,000	671,000,000	552,500,000
Derivative, Notional Amount	$ 5,590,000	$ 16,322,000	$ 15,002,000
Summary of Derivative Instruments [Abstract]
Cost of sales	(155,201,000)	(142,359,000)
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	10% or 20%
Oregon PGA Deferral Percentage	90.00%
Target Hedge Percentage	approximately 75%
Derivative, Gain on Derivative	8,500,000
Derivative, Loss on Derivative		5,400,000
Unrealized Loss On Derivatives	16,500,000
Derivative Asset, Fair Value, Net	16,600,000	8,300,000
Derivative Liability, Fair Value, Net	1,000,000	1,400,000
Derivative Fair Value Of Derivative Net	15,600,000	6,900,000	4,700,000
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	15,912,000	7,183,000
Less:Amounts deferred to regulatory accounts on balance sheet	(15,875,000)	(7,037,000)
Total gain (loss) in pre-tax earnings	37,000	146,000
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	(275,000)	(239,000)
Less:Amounts deferred to regulatory accounts on balance sheet	275,000	239,000
Total gain (loss) in pre-tax earnings	$ 0	$ 0