Derivative Instruments Gain (Loss) by Hedging Relationship, by Income Statement Location, by Derivative Instrument Risk (details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Derivative [Line Items]
Financial Derivative, Nonmonetary Notional Amount	297,925,000	359,135,000	297,925,000	359,135,000	389,225,000
Physical Derivative, Nonmonetary Notional Amount	241,150,000	322,675,000	241,150,000	322,675,000	552,500,000
Derivative, Notional Amount	$ 10,844,000	$ 17,171,000	$ 10,844,000	$ 17,171,000	$ 15,002,000
Summary of Derivative Instruments [Abstract]
Cost of sales	(58,280,000)	(59,142,000)	(213,481,000)	(201,501,000)
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	4,300,000	1,400,000	12,800,000
Derivative, Loss on Derivative				4,000,000
Unrealized Loss On Derivatives	11,300,000		11,300,000
Derivative Asset, Fair Value, Net	11,500,000	200,000	11,500,000	200,000
Derivative Liability, Fair Value, Net	800,000	9,700,000	800,000	9,700,000
Derivative Fair Value Of Derivative Net	10,700,000	9,500,000	10,700,000	9,500,000	4,700,000
Natural Gas Commodity [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	(5,379,000)	(16,139,000)	10,533,000	(8,956,000)
Less:Amounts deferred to regulatory accounts on balance sheet	(5,223,000)	(16,069,000)	10,652,000	(9,032,000)
Total gain (loss) in pre-tax earnings	(156,000)	(70,000)	(119,000)	76,000
Foreign Currency [Member]
Summary of Derivative Instruments [Abstract]
Cost of sales	454,000	(274,000)	(179,000)	513,000
Less:Amounts deferred to regulatory accounts on balance sheet	454,000	(274,000)	(179,000)	513,000
Total gain (loss) in pre-tax earnings	$ 0	$ 0	$ 0	$ 0